In muscle and livers of steers given a diet with sodium monensinate a significant decrease in cadmium content was observed. The concentration of manganese, copper, zinc, lead and iron in the analysed organs varied inconsistently. It seems from the results that, in tissues, monensinate influences the metabolism not only of monovalent cations but of polyvalent cations as well.

The records of 873 lambs from Ossimi and Barki backcrosses to Merino, and the first and second generations of their interbreeding were analysed. The traits included were: birth, weaning and yearling weights, first fleece weight and lamb mortality.

The interbred groups had about 10–15% lower body and fleece weights than their backcross parents, and almost double the lamb mortality. Differences between the interbred groups and the back-cross parents were predicted from the performance of purebreds, first crosses and backcrosses. There was good agreement between prediction and observation for birth and fleece weights, fair agreement for weaning and yearling weights, but lamb mortality increased more than expected.

Maternal heterosis seems to be more important than individual heterosis for body weight, and the reverse for fleece weight. Both components are large for lamb viability.

Live weights from birth to 3·5 years are reported for beef cattle reared under ranching conditions in Zambia. The 809 cattle were purebred Africanders, Angonis, Barotses and Borans and the reciprocal crossbreds of the latter three breeds born in 2 years. All animals born in the 1st year and half the males born in the 2nd year grazed natural grassland. The remaining males and all females born in the 2nd year received, in addition, dry season supplementary feed from 1·5 years of age.

The interaction of genotype with year-of-birth was important but not the interactions of genotype with management or sex. Purebred progeny of the introduced Africander breed were heavier than the progeny of the indigenous Angoni and Barotse breeds in both year-of-birth groups, but only heavier than progeny of the introduced Boran breed in the first group. On average, the Africander progeny had live-weight advantages of about 16% and 10%, and the Boran progeny advantages of about 12·5% and 5·5% over the purebred Angoni and Barotse progeny respectively. Heterosis estimates tended to increase with age, reaching levels of about 5 to 6% in the Barotse/Boran crosses at and after 1·5 years. Heterosis was not shown by the other crosses. The Barotse and Boran breeds had similar maternal effects which were superior to those of the Angoni breed.

An experiment was carried out at Bahia Blanca (38°44' S, 62°10' W) to estimate the seasonal variation in ovulation rate and its components shown by Lincoln ewes of constant live weight.

Twenty-three 5-year-old ewes were subjected to nine 17-day observation periods which were evenly spaced within 405 days.

Percentage of ewes showing oestrus and ovulation, incidence of multiple ovulations and ovulation rate were estimated for each period by using vasectomized rams and performing iaparoscopies.

Traits showed a similar seasonality which was presumably induced by the natural light regime to which the ewes became exposed before and during each observation period.

A significant and periodic relationship was found between each trait and the number of days elapsed from the longest day.

The predicted maximum values for each parameter were reached about 40 days before the shortest day. Prior to and after this date both the percentage of ewes showing oestrus and ovulation and the incidence of multiple ovulations declined so that the expected ovulation rate values became zero for a period of about 3 months before the longest day.

Two 7 × 7 Latin square experiments were carried out with British Friesian steers (mean initial live weight 360 kg). In Experiment 1 the effects of different levels of dried grass or concentrate on the intake of silage dry matter (DM) were compared, and in Experiment 2 the effect of a supplement containing various proportions of dried grass: concentrate on the intake of silage DM was examined. In both experiments the digestibility of the ration and the rate of passage of digesta were measured.

In Experiment 1, supplementation depressed intake of silage DM, the difference being significant (P<0·05) at 5·0 and 7·5 kg/day, but there were no significant differences in silage intake between supplements given at the same level. Intake of silage was also significantly lower (P<0·05) in Experiment 2 when a supplement was offered, but differences between supplements were not significant. Total DM intake was increased significantly (P<00·5) by supplementation in both experiments. Supplementation increased energy digestibility but decreased crude fibre digestibility. In Experiment 1 nitrogen digestibility was significantly lower (P<0·05) with dried grass than with concentrate supplementation, but in Experiment 2 supplementation increased the digestibility of nitrogen. In both experiments the mean retention time was shorter, the time for the highest rate of excretion of stained particles was lower, and the maximum rate of excretion higher for dried grass than for silage.

Six adult and six juvenile goats were used to estimate their feeding preferences when three grasses (ryegrass, barley and brome) and two legumes (clover and alfalfa) were tested. Each grass was separately tested with both clover and alfalfa. A comparison between alfalfa and clover was also performed. The plants were harvested just before their utilization, chopped into 4- to 6-cm pieces and offered to the animals in plastic baskets. Preferences were evaluated by means of a series of seven short-term trials. Each short-term trial consisted of two single-food presentations and one choice-presentation. In the first single-food presentation animals received one of the two plants to be tested. In the second single-food presentation they were offered the alternative plant species. In the choice presentation they received the two species simultaneously. During each presentation animals were allowed to eat for 20 min or take a maximum of 50 bites. In the single-food presentations bite rate, bite mass and intake rate of both juvenile and adult animals were influenced by the plant species offered. Indeed, all goats tended to display a higher intake rate and bite mass for grasses than for legumes. A grass/legume ratio of the intake rates was also computed for each grass-legume comparison. These ratios tended to be higher for juvenile than for adult goats. The results of the choice presentations indicated that food preferences were not affected by age as all goats preferred grasses to legumes and clover over alfalfa. This experiment showed that age may not play an important role in the development of food preferences.

The urine of pigs contains a substance with an anorexigenic effect when injected into pigs or rats. When injected into rats or pigs on ad libitum feeding a urine extract caused a reduction in food intake only when the extract had been obtained from the urine of satiated pigs, and not from hungry pigs. The pig urinary anorexigen there-fore appears to be similar in nature to the anorexigen extracted from rat urine. Like rat urinary anorexigen, its anorexigenic effect is largely dose dependent and it is soluble in distilled water. Rats injected with plasma from satiated pigs showed an anorexigenic reaction but injection of plasma from hungry pigs had no effect on food intake. The possible role of these anorexigenic substances in the control of voluntary food intake in the pig is discussed.

Two pedigree indexes were calculated for 754 Friesian/Holstein bulls born between 1974 and 1980 and tested by the Milk Marketing Board. Correlations between the indexes and the average progeny performance were used to compare the indexes calculated using information from different ancestors. The first index, or estimated predicted difference (EPD) was calculated as one-half the sire progeny test, known as an Improved Contemporary Comparison (ICC), plus one-quarter the maternal grandsire ICC. The second index or estimated ICC (EICC) was calculated from one-half the sire ICC plus one-half the dam cow genetic index (CGI). The correlations between the deregressed bull evaluations (DICC) and EPD, calculated from 310 bulls, were 0·40 for milk yield, 0·40 for fat yield and 0·39 for protein yield. The corresponding correlations between the DICC and EICC, calculated from 314 bulls, were 0·43, 0·40 and 0·41. The regression coefficients for predicting average progeny performance from the EPD index were 1·00 (s.e. 0·13), 0·97 (s.e. 0·12), 0·96 (s.e. 0·13), 1·09 (s.e. 0·12) and 1·08 (s.e. 0·10) for milk, fat and protein yield, fat and protein percentage respectively. Those for predicting progeny performance from the EICC index were 0·95 (s.e. 0·11), 0·81 (s.e. 0·10) and 0·84 (s.e. 0·10) for milk, fat and protein yield respectively. Although the correlations were lower than the expected values of 0·50 (EPD) and 0·55 (EICC) the regressions were near the expected value of 1. The results indicate that the indexes are useful as a preliminary means of selecting bulls prior to progeny testing.

Four groups of 10 indigenous goats, suckling indigenous or crossbred, single or twin kids, were used to study the effect of sucking stimulus on milk yield and composition during a 12-week suckling period and over the first 20 weeks of the subsequent milking period. During the suckling period, goats with twins produced more milk (F < 0·001) than those with singles. There was no effect of kid genotype in goats rearing twins but single crossbreds took 1·11 times more milk than indigenous. Goats with single kids had higher concentrations of fat (F < 0·001), protein (F < 0·05) and lactose (F < 0·05) in milk than did those with twins. Growth rate of kids was related to differences in milk intake, with singles higher than twins (F < 0·001) and crossbred singles higher than indigenous singles (F < 0·05). It is concluded that the indigenous breed can respond to the increased sucking demand of twins but not sufficiently to meet their needs. During the milking period the mean yield was reduced to about one-third and was not dependent on the corresponding yield in the suckling period. There were minor differences of milk composition associated with number or genotype of kids suckled.

The suggestion has been made (e.g. Anon, 1961; Brown, 1964; Spedding and Brown, 1961; Wixey, 1965) that a method of overcoming the inability of ewes to rear twin lambs well, may be to wean one lamb out of each pair at 2–4 weeks of age. The weaned lamb would be reared on concentrates and/or grass, and the remaining lamb, which would have access to the entire milk supply of the ewe, might then show a similar rate of growth to that of a lamb reared as a single from birth. Studies have also been made of the effect of the removal of one lamb out of twin pairs at 9 weeks of age (Cunningham and Maxwell, 1966) and at 12–16 weeks of age (Cunningham, 1964).

1. Analyses of records of eight-week body weight in broiler chickens have been carried out to estimate the effect of management level (measured by mean body weight of all varieties on each farm) on the components of variance due to differences between and within varieties, and to find out if there is any evidence of genotype-environment interaction.

2. It was found that as management improved, the between-variety genetic variance remained constant or possibly increased whilst the withinvariety (genetic and environmental) variance decreased markedly. The cause of these regressions is not known.

3. In four cases out of six there were significant genotype-environment interactions. In two cases, the genetic correlation between the performance of varieties on different locations was significantly different from 1·0.

4. It is suggested that on the basis of these findings it would be necessary to select between varieties on records taken from chickens maintained under conditions similar to those in which they will eventually be used. However, fewer chickens would be required to measure, with a predetermined level of accuracy, mean differences on well managed farms than on poorly managed ones.

In two experiments cows with access to self-feed grass silage were offered concentrates either twice daily in the milking parlour at a fixed level (controls) or in addition given free-access to a concentrate dispenser sited in the self-feed area (dispenser). A time-lapse mechanism on the dispenser limited successive 1 kg feeds to a minimum of 10 min in experiment 1 and 5 min in experiment 2. The ‘dispenser’ cows had significantly greater total concentrate intakes than had the controls (10·4 v. 7·1 kg/day in experiment 1, 13·4 v. 7·3 kg/day in experiment 2), but there was a large variation in intake between individuals. Access to the dispenser increased milk yields only slightly, reduced milk fat concentration and increased milk protein concentration and live-weight gain. Following turnout to grass in the spring, there was evidence that the cows that had been on the dispenser treatment showed a faster rate of decline in milk yield than did the controls, and this was supported by lower lactation yields in the dispenser group.

Eight change-over design experiments (each a duplicated 3 × 3 Latin square design using six rumen-fistulated wether sheep, live weight 50 to 60 kg) measured rumen fermentation patterns for 24 perennial ryegrass silages. Sheep were offered 800 g dry matter (DM) per day of each silage in two equal meals at 09.00 and 17.00 h. Samples of rumen liquor were taken on days 19 and 21 of each 21-day period, at 08.50 h and at 1·5-h intervals until 16.30 h. Rumen samples were analysed by gas chromatography; silages by high-performance liquid chromatography and by near infra-red reflectance spectroscopy (NIRS) using samples scanned after drying at 100°C (NIRSdry) or in the fresh state (NIRSwet).

Mean intake of DM was 737 g/day. The range of silage composition was as follows (mean, range, s.d., g/kg DM unless specified): metabolizable energy (ME MJ/kg DM) 11·1, 8·8 to 12·6, 0·81; pH 4·0, 3·6 to 5·0, 0·34; lactic acid 86, 4 to 139, 42·6; butyric acid 4·7, 0·1 to 46·7,10·2. Rumen measurements varied substantially both diurnally and between silages. Mean diurnal rumen values for the 24 silages (mean, range, s.d.) were: pH 6·76, 6·55 to 7·09, 0·155; ammonia (mg/l) 132, 70 to 247, 47·7; total volatile fatty acids (TVFA mmol/l) 58·2, 45·8 to 72·0, 8·97; (acetate+butyrate)/propionate (ABP) 3·2, 2·2 to 4·8, 0·56.

Partial least-square models were developed to predict rumen fermentation (means for six sampling times) using either the silage chemical composition (CHEM g/kg DM unless specified: DM, ME (MJ/kg DM), crude protein (CP), ammonia (NH3, g N per kg total N), neutralizingvalue (meq per kg DM), sugar, lactic, formic, acetic, propionic and butyric acids and ethanol) or silage NIRSdry or NIRSwet. Prediction performance was assessed comparing values for R2, standard error of cross validation (SECV) and SD/SECV (s.d. of reference population! SECV) obtained by the ‘leave one out’ cross validation method. NIRSwet gave slightly better prediction accuracy overall than NIRSdry but both were superior to prediction from chemical composition. Values for R2, SECV and SD/SECV for pH were 0·23, 0·14, 1·09; 0·76, 0·08, 2·01 and 0·72, 0·08, 1·89 for CHEM, NIRSdry and NIRSwet respectively. Corresponding values for rumen ammonia (mg/l) were 0·48, 35·2, 1·35; 0·69, 27·1, 1·76 and 0·70, 26·3, 1·81; for TVFA 0·52, 6·73, 1·33; 0·80, 4·06, 2·21 and 0·93, 2·47, 3·63; for rumen ABP ratio 0·69, 0·32, 1·78; 0·76, 0·30,1·88; 0·72, 0·30,1·85. The silage predictors with greatest influence in the CHEM model for rumen ABP ratio were sugar, CP and lactic acid (negative) and butyrate and ethanol (positive). NIRS shows considerable promise as a means of predicting rumen fermentation of animals given grass silage diets.

Two trials were conducted with eight yearling camels with an average intial body weight of 300 kg, to evaluate protein and energy values of lucerne hay and barley grains. In each trial, eight animals were randomly allotted to two different dietary treatments of coarsely ground lucerne hay or lucerne hay + barley grain (50:50) in such a way that two animals in each of the two blocks received the same ration. Each trial consisted of a 10-day preliminary period followed by a 7-day collection period during which total urine and faeces collections were made, and samples were processed and composited for later analysis.

All animals consumed daily an average of about 5 kg food divided in two equal meals. The apparent digestibility coefficients for organic matter, crude protein, neutral-detergent fibre and cellulose of the lucerne hay ration improved respectively from 0·615, 0·662, 0·455 and 0·555 to 0·736, 0·655, 0·547 and 0·589, as a result of incorporating 500 g/kg barley grain in place of hay in the diet. Even though there was no difference in the proportion of nitrogen retained relative to intake, the proportion of nitrogen retained relative to that absorbed was higher (P < 0·05) in the lucerne + barley group (0·769) than in the lucerne-only group (0·747). On a dry-matter basis, the feeding value in camels of digestible protein (g/kg), total digestible nutrients (g/kg), digestible energy (MJ/kg), metabolizable energy (MJ/kg), net energy maintenance (MJ/kg), net energy lactation (MJ/kg) and net energy gain (MJ/kg) were respectively 118, 552, 10·0, 8·4, 5·4, 5·0 and 2·1 for lucerne hay and 80, 800, 14·6, 12·1, 8·4, 8·8 and 5·0 for barley grain (calculated by difference).

An experiment was carried out to evaluate the effects of forage type and level of concentrate supplementation on forage intake, diet apparent digestibility, purine excretion and milk production. Twelve crossbred cows (Bos taurus × Bos indicus), in early lactation, were allocated to the following six dietary treatments: maize-lablab forage (ML) or oat-vetch forage (OV), offered ad libitum, and supplemented with either 0, 2·5 or 5·0 kg per cow per day of a supplement (wheat middlings). A four-period, partially balanced, change-over design was used and the treatments were arranged as 2 × 3 factorial.

Mean organic matter (OM) intake was 670 g higher with cows on ML-based diets compared with those on OV-based diets (P <0·02). The apparent digestibilities of crude protein (CP) and neutral detergent fibre (NDF) were similar for cows given ML- or OV-based diets but the apparent digestibility of OM was higher for ML diets (P <0·05). Values of the degradation parameters (a, b and c) of DM and NDF were greater for ML forage than for the OV forage. Forage type did not affect daily milk yield nor excretion of purine derivatives in urine used to estimate microbial-nitrogen supply (P >0·05). The concentration of milk fat and total solids in the milk were similar for the two forage types offered but the concentration of milk protein was slightly higher for the cows given ML-based diets (P <0·05).

Daily OM intake increased by 3·75 and 2·70 kg per cow per day (P <0·001) respectively, when the amount of concentrate increased from 0 to 5·0 kg per cow per day for the ML- and OV-based diets. The CP apparent digestibilities of the diets were higher when the diets were supplemented with concentrates but there was no effect of supplementation on the apparent digestibilities of OM and NDF. The supply of microbial-nitrogen increased linearly with increasing level of concentrate supplementation (P <0·05). Milk yield increased linearly when the level of concentrate supplement increased from 0 to 5 kg (P <0·001), resulting in 0·39 and 0·29 kg more milk per day per kg additional concentrate given in cows on ML and OV, respectively. There was also a tendency for a quadratic effect (P <0·12), especially with ML diets, showing that when the level of concentrate increased from 0 to 2·5 or from 2·5 to 5·0 kg/day, the milk yield increased respectively by 0·62 and 0·15 kg/day per kg additional concentrate given.

Factors affecting survival to first and second calving and successful completion of a > 168-day first lactation were assessed in 3075 purebred and crossbred dairy heifer calves. Growth, disease, frequency, reproduction, calving, udder and lactation traits were examined in females of a breeding project conducted jointly at five research stations (herds) of Agriculture Canada. Losses included mortalities and non-discretionary culling. About 0·23 of potential heifers were culled or died before first calving, and 0·25 of those calving once did not calve a second time. Results from retrospective selection index and stepwise linear logistic analyses showed that predictability of culling prior to 308 days post partum was poor. With few exceptions, survival rates from birth to 82 weeks varied among herds (P < 0·001) and among lines (P < 0·05). Heterosis for the probability of completing a lactation and of survival to second calving was significant (P < 0·05) and positive (0·05 to 0·09). Heavier heifers were more likely to survive to first calving. Sire's estimated breeding values (SEBV) for milk yield and fat, protein and lactose concentration were not important in predicting survival to first calving. SEBV lactose was negatively associated with survival after first calving as predicted from data available at most preceding stages of life. An age greater than 82 weeks at last insemination was associated with a lower probability of survival to first and second calving (P < 0·001). Cows which conceived for a second gestation and subsequently aborted had a lower probability of survival to second calving than cows which did not abort (0·57 v. 0·76, P < 0·01). The only continuous traits with large effects on survival or the probability of completing a first lactation were days to last insemination (a measure of fertility) and milk yield. It was concluded that (1) there is considerable scope for improved management to increase survival in early life by prevention of calfhood diseases; (2) losses in early life do not bias sire evaluation on first lactation records; (3) improved reproductive success would greatly enhance overall survival rates; and (4) crossbreeding could have a large impact on overall herd profitability through increased survival.

As a result of the genetic selection for prolificacy and the improvements in the environment and farms management, litter size has increased in the last few years so that energy requirements of the lactating sow are greater. In addition, selection for feed efficiency of growing pigs is also conducted in maternal lines, and this has led to a decrease in appetite and feed intake that is extended to the lactation period, so the females are not able to obtain the necessary energy and nutrients for milk production and they mobilize their energetic reserves. When this mobilization is excessive, reproductive and health problems occur which ends up in an early sow culling. In this context, it has been suggested to improve feed efficiency at lactation through genetic selection. The aim of this study is to know, in a Duroc population, the genetic determinism of sow feed efficiency during lactation and traits involved in its definition, as well as genetic and environmental associations between them. The studied traits are daily lactation feed intake (dLFI), daily sow weight balance (dSWB), backfat thickness balance (BFTB), daily litter weight gain (dLWG), sow residual feed intake (RFI) and sow restricted residual feed intake (RRFI) during lactation. Data corresponded to 851 parities from 581 Duroc sows. A Bayesian analysis was performed using Gibbs sampling. A four-trait repeatability animal model was implemented including the systematic factors of batch and parity order, the standardized covariates of sow weight (SWf) and litter weight (LWs) at farrowing for all traits and lactation length for BFTB. The posterior mean (posterior SD) of heritabilities were: 0.09 (0.03) for dLFI, 0.37 (0.07) for dSWB, 0.09 (0.03) for BFTB, 0.22 (0.05) for dLWG, 0.04 (0.02) for RFI and null for RRFI. The genetic correlation between dLFI and dSWB was high and positive (0.74 (0.11)) and null between dLFI and BFTB. Genetic correlation was favourable between RFI and dLFI and BFTB (0.71 (0.16) and −0.69 (0.18)), respectively. The other genetic correlations were not statistically different from zero. The phenotypic correlations were low and positive between dLFI and dSWB (0.27 (0.03), dSWB and BFTB (0.25 (0.04)), and between dLFI and dLWG (0.16 (0.03)). Therefore, in the population under study, the improvement of the lactation feed efficiency would be possible either using RFI, which would not have unfavourable correlated effects, or through an index including its component traits.

Standard artificial insemination (AI) using a speculum in dairy goats does not result in acceptable fertility rates in nulliparous does. An explanation might be the difficulties to pass the cervical canal in nulliparous females with the insemination gun, increasing the time needed for semen deposition. Nulliparous Alpine dairy goats were used to evaluate whether time interval from insertion to withdrawal of the speculum is a factor influencing pregnancy rates to first AI with frozenthawed semen. Oestrus was synchronized using fluorogestone acetate intravaginal sponges (FGA, 40 mg) for 11 days, associated with 50 mg i.m. of cloprostenol and 250 IU i.m. eCG 48 ± 2 h before sponge removal. In the first experiment (n = 52; 3 herds), the average duration of the AI procedure was 42 ± 10 s, with a median of 39 s. AI performed in less than 39 s resulted in higher pregnancy rates (75%, n = 28) than AI lasting for more than 39 s (46%, n = 24). In the second experiment, does (n = 325; 5 herds) were randomly assigned into two treatment groups according to a short (20 s) or long (60 s) AI procedure. We showed that the duration of AI affected fertility after a first insemination, and that pregnancy rate was significantly improved using a short-duration AI (61.2%; n = 169) compared with a long-duration AI (44.2%; n = 156). We have previously shown in the ewe that genital stimulation during AI enhanced uterine motility. Other authors reported a negative correlation between increased uterine motility at the time of AI and fertility rates in small ruminants. The results of this study suggest that rapid semen deposition may limit the reflex activation of uterine contractions provoked by the speculum and the movement of the insemination gun, and thus ameliorates reproductive performance to first AI in nulliparous goats.

Nitric oxide (NO) and protein kinase C (PKC) are involved in the activation of mammalian oocytes, although their role in the exit from the metaphase II stage and cortical granule (CG) exocytosis is still not fully understood. The aim of this study was to verify whether the NO-donor together with specific PKC-activators induce the complete activation of porcine oocytes assessed as meiosis resumption and a cortical reaction. Pig maturated oocytes were treated with the NO-donor S-nitroso-N-acetylpenicillamine (SNAP, 2 mM) or PKC-activators such as phorbol-12-myristate-13-acetate (PMA, 100 nM), 1-oleoyl-2-acetyl-sn-glycerol (OAG, 400 μM) and l-α-phosphatidylinositol-3,4,5-trisphosphate dipalmitoyl heptaammonium salt (DPAM, 2 μM). To study the combined effect of NO-donor and PKC-activators, aliquots of oocytes were also incubated with SNAP (0.5 mM) together with PKC-activators at the same concentration as above (SNAP–DPAM, SNAP–OAG and SNAP–PMA groups). After invitro maturation, an aliquot of oocytes was placed in a fresh medium without NO-donor or PKC-activators (Control group). Another aliquot of oocytes was activated by calcium ionophore A23187 (25 μM, 5 min). The results showed that 0% of the control oocytes reassumed meiosis. However, both the PKC-activators (DPAM 44.0 ± 10.0%, OAG 63.3 ± 1.0% and PMA 45.0 ± 16.5%) as well as the NO-donor alone (48.7 ± 21.0%) significantly induced exit from MII. Interestingly, the combination of PKC-activators and SNAP mainly restrained to the meiosis resumption (SNAP–OAG 0, SNAP–DPAM 17.4 ± 2.5% and SNAP–PMA 38.4 ± 8.5%). Control oocytes did not show a cortical reaction and the area occupied by CG reached 25.9 ± 1.7%, whereas CGs were partially released after Ca2+ ionophore treatment (13.0 ± 3.2%). Treatment with PKC-activators induced a cortical reaction compared with the control group (8.6 ± 2.5, 6.7 ± 1.9 and 0.7 ± 0.4%, respectively, for DPAM, OAG and PMA groups). However, treatment with the NO-donor alone (SNAP group 17.2 ± 2.2%) or combined with any PKC-activator prevented cortical reaction (SNAP–DPAM 20.7 ± 2.6%, SNAP–OAG 16.7 ± 2.9% or SNAP–PMA 20.0 ± 2.4%). Besides, meiosis resumption was not always accompanied by a cortical reaction, indicating that these two activation events are independent. In conclusion, PKC-activators alone induce CG exocytosis to the same degree as calcium ionophore. However, an NO-donor alone or combined with PKC-activators is not able to induce a cortical reaction in pig oocytes.

In the dairy industry, excess dietary CP is consistently correlated with decreased conception rates. However, the source from which excess CP is derived and how it affects reproductive function in beef cattle is largely undefined. The objective of this experiment was to determine the effects of feeding excess metabolizable protein (MP) from feedstuffs differing in rumen degradability on ovulatory follicular dynamics, subsequent corpus luteum (CL) development, steroid hormone production and circulating amino acids (AA) in beef cows. Non-pregnant, non-lactating mature beef cows (n=18) were assigned to 1 of 2 isonitrogenous diets (150% of MP requirements) designed to maintain similar BW and body condition score (BCS) between treatments. Diets consisted of ad libitum corn stalks supplemented with corn gluten meal (moderate rumen undegradable protein (RUP); CGM) or soybean meal (low RUP; SBM). After a 20-day supplement adaptation period, cows were synchronized for ovulation. After 10 days of synchronization, gonadotropin releasing hormone (GnRH) was administered to reset ovarian follicular growth. Starting at GnRH administration and daily thereafter until spontaneous ovulation, transrectal ultrasonography was used to diagram ovarian follicular growth, and blood samples were collected for hormone, metabolite and AA analyses. After 7 days of visual detection of estrus, CL size was determined via ultrasound. Data were analyzed using the MIXED procedures of SAS. As designed, cow BW and BCS were not different (P⩾0.33). Ovulatory follicular wavelength, antral follicle count, ovulatory follicle size at dominance and duration of dominance were not different (P>0.13) between treatments. Cows supplemented with CGM had greater post-dominance ovulatory follicle growth, larger dominant follicles at spontaneous luteolysis, shorter proestrus, and larger ovulatory follicles (P⩽0.03) than SBM cows. No differences (P⩾0.44) in peak estradiol, ratio of estradiol to ovulatory follicle volume, or plasma urea nitrogen were observed. While CL volume and the ratio of progesterone to CL volume were not affected by treatment (P⩾0.24), CGM treated cows tended to have decreased (P=0.07) circulating progesterone 7 days post-estrus compared with SBM cows. Although total circulating plasma AA concentration did not differ (P=0.70) between treatments, CGM cows had greater phenylalanine (P=0.03) and tended to have greater leucine concentrations (P=0.07) than SBM cows. In summary, these data illustrate that excess MP when supplemented to cows consuming a low quality forage may differentially impact ovarian function depending on ruminal degradability of the protein source.