Thirty-eight multiparous sows were used to ascertain whether a high (4 kg/day), compared with a low (2 kg/day) food level affected early embryonic survival. To avoid any effect on ovulation rate the treatments were imposed 3 days after mating (2 days after presumed ovulation) and continued until the sows were killed 30 days after mating. Sows which were given the high food level gained more than twice as much body weight as those on the low food level, but ovulation rates, embryo numbers, embryo body sizes and embryo survival rates were similar for both feeding levels. It is concluded that, if necessary, multiparous sows may be fed higher than normal food levels in early pregnancy without prejudice to embryonic survival.

Three treatments were imposed on three groups of four boars from 26 to 40 weeks of age: a mating frequency of six copulations per week, housed near sexually receptive gilts (M + ♂); not mated, housed near sexually receptive gilts (NM + ♂); and not mated, isolated from female pigs (NM – ♂ ). The M + ♂ boars had similar semen characteristics from 49 to 57 weeks of age to the NM + ♂ and NM – ♂ boars. However, the M + ♂ boars achieved a significantly greater number of copulations (P < 0·05) and spent significantly longer ejaculating (P < 0·05) during the mating tests conducted from 49 to 57 weeks and from 66 to 70 weeks of age than the NM – ♂ boars. It is concluded that isolating young post-pubertal boars from female pigs will reduce their subsequent copulatory performance. Further, mating at a high frequency from 26 to 40 weeks of age does not appear to seriously affect subsequent semen quality.

An experiment was conducted to show the effectiveness of selection for improved food conversion ratio on ad libitum group feeding. Selection (32 ♀♀ and 8 ♂♂) and unselected control (32 ♀♀ and 16 ♂♂ lines were maintained for seven generations at the rate of one per year. Progeny were fed ad libitum from 27 to 82 kg live weight: boars singly or in pairs, and gilts in litter groups. Selection was on pen average food conversion ratio (food/live-weight gain), recalculated as each pig reached 82 kg.

In spite of selection differentials averaging 0·61 s.d. per generation, there was no response (selection minus control) in food conversion at Generation 6 (−0·03, s.e. 0·08). However, there were correlated increases in daily live-weight gain (56, s.e. 18 g), daily food intake (145, s.e. 59 g) and ultrasonic backfat (2·4, s.e. 0·4 mm). In Generation 7, 146 full-sib pairs (male castrate and gilt) were tested on ad libitum or scale (0·77 g/g ad libitum daily food intake) feeding. Line by feeding regime interactions were absent for all traits except killing-out proportion and belly thickness.

The increased fatness of the selection line on ad libitum feeding was retained on the scale (2·2 v. 2·4, s.e. 10 mm), suggesting a primary difference in partition of nutrients rather than intake. The selection procedure adopted was not successful in improving food conversion, but no clear conclusions could be drawn from the experiment. Uncertainty remains as to the value of group food consumption measurements in selection programmes.

The value of several live animal measurements for predicting carcass lean content was assessed on 97 Hereford bulls. The bulls were from a series of performance tests extending over a period of 4 years. The measurements made were live weight, ‘Weighband’ estimate of live weight, skin-fold thickness at the 13th rib, anal-fold thickness and Danscanner and Scanogram ultrasonic fat area. All measurements, except anal-fold thickness, showed satisfactory repeatability from one day to the next (0·45 to 1·00). Ultrasonic measurements showed the highest correlations with carcass lean content (0·22 to 0·66; corresponding residual s.d.'s, 13·87 and 26·46 g/kg). The most precise prediction of lean content was achieved with live weight and ultrasonic measurements in a multiple regression. The precision achieved and best anatomical sites for ultrasonic measurement varied with the group of bulls (highest R2 values 0·61 to 0·77; corresponding residual s.d. 's, 25·75 and 22·47 g/kg). The Scanogram machine produced more repeatable results than the Danscanner. When compared on the same animals Scanogram measurements gave slightly more precise prediction of carcass lean content than Danscanner measurements. Over all groups of bulls the two machines produced results of similar accuracy. Accounting for precision of estimating carcass lean content, response to selection for leanness was estimated to be 0·0034 to 0·0049 of the mean per annum for bulls of about 400 or 500 days of age.

The effect of rate of growth on the development of animals is examined in terms of it being related to variation from a pattern of development described by the allometric hypothesis. For this purpose, aliometry is expressed in terms of an extension to the shape/size concept originally proposed by Mosimann.

It is shown that such an effect of rate of growth would bias estimates of the development pattern, depending on the experimental design. However, within the framework of the method, a procedure for both removing the bias and actually estimating the effect of rate of growth on development is available.

A previously described test for one type of deviation from aliometry is shown to be incorrect by simulation.

An alternative test for the adequacy of the allometry hypothesis is developed, based on factor analysis of residual matrices from multivariate analysis of variance (the latter being used so that effects of treatment and concomitant variables can be taken into account).

One hundred Friesian heifers were tail-painted between 14 and 21 days after calving. Once a week the paint strip was renewed if any paint had been removed. Over the whole period of observation the ovulation detection rate by definite signs of oestrus was high (0·79), whilst the proportion of silent ovulations detected by tail paint removal was low (0·10). In addition, tail paint was not removed on 0·28 of the occasions when definite oestrus with ovulation occurred and on 0·26 of the occasions when all the paint was removed it was not associated with any reproductive event. In practice, the critical time for tail paint to be effective is during the service period. Again, tail paint identified fewer (P < 0·001) ovulations than definite signs of oestrus (0·66) and had a significantly higher false positive rate (P < 0·001). Month of calving did not affect these results but the accuracy of tail paint declined as the season progressed (P < 0·001). False positive indications were not associated with individual animal characteristics. In a second trial 43 cows were tail-painted and 43 were not. There was no significant difference in the mean number of days from calving to first insemination or successful pregnancy between the two groups. It is concluded that in these trials tail paint was not an effective or reliable aid or alternative to oestrus detection.

An analysis was performed on data from three breeds recorded at the Pig Testing Station in Antrim in order to estimate and apportion variation in the measure of efficiency considered here, namely the daily food consumption after allowance had been made for maintenance and production requirements and other fixed effects. Results suggest that a considerable proportion of the variation in residual consumption is due to genetic causes (h2 = 0·3) and that selection to exploit this variation would result in an appreciable reduction in food costs. There were indications of considerable litter effects upon the trait.

Photographs of ultrasonic images of 10 animals were taken. Two replicate photographs were taken at each of four body positions (10th rib, 13th rib, 3rd lumbar and hindquarter) on both sides of the body in the morning and the afternoon of the day of scanning. Several measurements were taken on each photograph by an experienced interpreter. Replicate photographs failed to account for all possible sources of measurement error. Since neither time of day nor side of the body affected the mean value, taking observations at different times of the day or on both sides of the body could permit most sources of measurement error to be taken into account. Variation due to errors of measurement and differences among animals are presented. The residual error distribution contained several extreme outliers.

It was concluded that a better understanding of all the sources of bias and error will be needed if ultrasonic measurements are to be more widely used.

The effects of source of protein on performance and nitrogen metabolism were studied in pigs weaned at 21 days of age. All diets contained 190 g crude protein and 14·6 MJ digestible energy per kg, and had a similar essential amino acid composition. Sources of protein were a combination of soya bean meal, fish meal and dried skim milk which was compared with soya bean meal alone, or in combination with either fish meal or dried skim milk. Seven groups of pigs (four pigs per group) received each diet ad libitum until 56 days of age. Performance was similar with the combinations of sources of protein, but with soya bean meal alone, food intake and growth rate were reduced (P < 0·05), but food conversion efficiency was not affected. Nitrogen metabolism was studied in seven pigs per diet given a restricted intake. Under these conditions, protein source had no effect on performance or retention and apparent digestibility of nitrogen. Nitrogen retention increased (P < 0·05) between 35 and 49 days of age, and was affected by the duration of the balance period (P < 0·01). In a second experiment, imparting a fish-like odour to the diet with soya bean meal as the sole source of protein by the addition of a fish oil did not affect food intake or performance.

These results indicate that a mixture of protein supplements in the diet of pigs weaned at 21 days of age may be unnecessary.

In three experiments 250 high-yielding dairy cows were fed for 18 weeks after parturition either a low-protein (LP) diet containing 150 to 160 g crude protein per kg or a high-protein (HP) diet containing 190 to 200 g crude protein per kg. In all three experiments cows were fed an average of 2·6 to 2·9 kg crude protein per day on the LP diet and 3·3 to 3·7 kg crude protein per day on the HP diet. Inclusive of maintenance, crude protein intake was, on average, 71 to 83 g crude protein per kg milk on the LP diet and 84 to 112 g crude protein per kg milk on the HP diet.

Protein intake did not affect the post-partum decrease in body weight; however, cows in their 4th and later lactations lost significantly more weight than cows in their 2nd and 3rd lactations (P < 0·01). Number of lactation did not affect the levels of rumen fluid ammonia or plasma urea, but older cows had significantly higher milk yields than younger ones. In all the experiments the first oestrus was observed, on average, between 38 and 43 days after parturition. The first insemination was carried out, on average, between 69 and 75 days after calving. Protein intake or age did not affect the intervals between parturition and the first observed oestrus or insemination. Proportional conception rates of cows fed the LP and HP diets were 0·566 and 0·431, respectively (P < 0·05). Conception rates of cows in their 2nd and 3rd lactations were 0·582 and 0·515 for cows on the LP and HP diets, respectively, whereas conception rates of cows in their 4th and later lactations were 0·526 and 0·288, respectively (P < 0·02). Within the HP-fed group the difference in conception rate between cows in their 2nd and 3rd lactations and those in their 4th and later lactations was also significant (P < 0·01). The proportion of cows pregnant 126 days after parturition was 0·786 and 0·645 for cows fed the LP and HP diets, respectively (P < 0·05). The proportion of cows in their 2nd and 3rd lactations which were pregnant, was 0·792 and 0·702 for cows of the LP and HP groups, respectively. Pregnancy rates for cows in their 4th and later lactations were 0·769 and 0·515 in the LP and HP groups, respectively (P < 0·05).

Post-partum changes in the concentration of progesterone, oestradiol-17β and prolactin were measured by radioimmunoassay in the blood plasma and milk of 28 buffaloes. The mean concentration of progesterone in the plasma of normal animals was 0·24 ± 0·04 μ.g/1 on the day of calving and decreased linearly during the post-partum period, until the complete regression of the residual corpus luteum of pregnancy occurred, when the plasma concentration was recorded as 0μ05 to 0μ08 μg/l. The concentration at a silent oestrus was 0μ17 ± 0·02 μ.g/1. The milk progesterone profile was parallel to that of plasma but the level was 2 to 4 times higher.

The mean concentration of oestradiol-17β in plasma was 41·0 ± 2·34 ng/1 on the day of calving; it declined significantly by day 1 post partum (P < 0·001) and fluctuated between 8 and 16 ng/1 until oestrus, when the concentration was approximately 25 ng/1. The oestradiol-17β concentration in milk was significantly higher than that of plasma on the day of calving. During the first 20 days post partum, a similar concentration of oestradiol-17β was maintained in both fluids but thereafter the concentration in milk was 2 to 3 times that of plasma.

The mean concentration of prolactin in plasma was 212·6± 19·08 μg/1 on the day of calving and then declined and fluctuated between 70 and 270 μg/1 during the rest of the period. A minor elevation occurred around oestrus. The prolactin concentration for the first 2 days post partum in milk was significantly higher than that in plasma but during the rest of the period it was similar to that in plasma.

The progesterone concentrations were slightly lower in anoestrous animals than in those cycling. The concentration of prolactin was significantly higher in multiparous animals (P < 0·001), whilst the progesterone and oestradiol values were similar in primiparous and multiparous animals.

Thirty-three crossbred boars, 47 to 58 days of age, were randomly allocated to receive maize-soya bean meal diets containing 0·05, 0·15 or 0·30 mg selenium per kg. Body weights, testicular widths, and blood samples from vena cava puncture were taken at regular intervals. Libido was subjectively scored upon exposure to ovariectomized-oestrogenized gilts. Seven animals from each group were slaughtered at 9 months of age and selected reproductive structures were retrieved. Analysis of the relationships among body weight, libido and plasma testosterone levels indicated that differences (P < 0·01) existed between treatments, as analyzed over time, but that the overall treatment effect was not significant. Testicular widths were also found to be different (P < 0·05) over time. Values for all four criteria as measured over time were greater for boars fed 0·05 mg selenium per kg than for those fed 0·15 which were in turn greater than those fed 0·30. Post-mortem examination showed no treatment differences (1) in testis weights; (2) spermatozoan concentrations within the capita, corporea or caudae segments of the epididymis and (3) spermatozoan morphology examined within the caudae epididymis. Also testis lengths, weights, circumferences and spermatozoan concentrations were not significantly different between treatments. These results suggest that boars fed selenium at 0·15 or 0·30 mg/kg may exhibit some signs of retarded sexual development for a short period preceding the onset of sexual maturity

Feedlot performance and carcass characteristics were examined in bulls and steers with and without a subdermal Silastic capsule containing oestradiol-17β-dipropionate. Castration and/or oestrogen treatment was imposed at approximately 8 months of age. The implants were removed 56 days before slaughter, i.e. 140 days after the trial commenced. Bulls gained more rapidly (12·9%), converted food to live-weight gain more efficiently (18·0%) and yielded leaner carcasses than did steers (P < 0·05). The oestrogenic implant elevated serum oestradiol concentrations substantially (> ninefold) over that of bulls and steers and induced a castration-response in the former. Serum luteinizing hormone, testosterone and testicular growth were suppressed (P < 0·05) during the first 140 days of the trial in bulls, but returned to normal following implant removal. This response was paralleled by a reduction in average daily gain (P < 0·05) and food: gain ratio (P < 0·10). Contrary to expectations, average daily gain and food: gain ratio were not significantly improved in implanted steers. Oestrogen treatment reduced hot carcass weight, loin eye area and quality grade in both bulls and steers; the last as a result of decreased marbling and internal fat deposition. Results of this study suggest that excessive oestrogen as provided in this study via the implant fails to improve feedlot performance and carcass merit in steers and may, in fact, diminish the inherent anabolic attributes of the intact male. Additional studies are required to understand the complex interactions of androgens and oestrogens in the regulation of body growth and composition of male cattle.

The performance of 200 F1 Friesian ♂ × zebu ♀ and 90 zebu heifers on 14 dairy cooperative farms near Addis Ababa was compared over a 2-year period. The farms varied in management and feeding but in general the standards were low. Each farm had zebu and Friesian × zebu cows given the same management and feeding. Measurements were made of milk production traits of economic importance, including physiological and behavioural factors important for management purposes.

The Friesian ♂ × zebu ♀ crossbred heifers showed an advantage in having an earlier age at puberty and at first calving, higher milk production, longer lactations, better disposition at milking and better reproductive performance. The calves from these crossbred heifers were larger at birth but there were more problems at calving. The zebu heifers withstood better the two periods of drought that occurred during the study. No significant differences were found in disease incidence, parasitic resistance, mastitis incidence or mortality. The interval between oestrus was normal in the F1 heifers but longer in the zebus. The duration of gestation was much longer in the zebus (mean 291 days). The duration of oestrus was 4·5 h for the zebu and 10·0 h for the F1 heifers, the latter being-much longer than the mean of 7·4 h reported in the literature. The F1 heifers showed the first oestrus after calving much sooner than did the zebus.

In the first experiment there were significant correlations between the average product of the length and width of the boar's testicles and the sperm output of the boar under a high collection frequency over two 6-h periods and over a 6-week period (r = +0·80, d.f. = 4, P < 0·05 and r = +0·77, d.f. = 7, P < 0·05, respectively). In the second experiment there were no significant differences in the fertility or fecundity of mature boars that had either two or six copulations per week over a 25-week period. However, there was a significant correlation between the average width of the boar's testicles and the fertility of the boar under the high mating frequency (r = +0·74, d.f. = 8, P < 0·05). There were also significant correlations between the number of copulations achieved in two mating tests and the number of copulations achieved and the refusal rate to mate under the high mating frequency (r = +0·86, and r = –0·89, respectively, d.f. = 6, P < 0·01). The implication of these results to the development of tests to predict mating performance of boars is discussed

Twenty bull calves were assigned to one of four treatment groups: 1) intact bulls; 2) intact bulls implanted with oestradiol dipropionate; 3) steers, and 4) steers implanted with oestradiol dipropionate. Subcutaneous adipose tissue was obtained by biopsy 5 months after implantation. Experimental treatment did not alter (P > 0·05) mean adipose cell volume, diameter or cell number per g adipose tissue. Soluble protein content of adipose cells from bulls was increased by implantation, but not in steers. In vitro rates of fatty acid synthesis were higher in oestrogen-implanted cattle compared with nonimplanted cattle when expressed per g adipose tissue, but not when expressed per cell. Maximal activities of the lipogenic-related enzymes, acetyl coenzyme A carboxylase, adenosine triphosphate-citrate lyase, aconitate hydratase and NADP-isocitrate dehydrogenase were higher in implanted compared with nonimplanted cattle when the activities were expressed per g tissue and acetyl coenzyme A carboxylase and aconitase were also higher when expressed per adipose cell. Bulls and steers had the same basal and stimulated lipolytic rates and implantation of oestradiol dipropionate had no effect on either basal or stimulated lipolytic rate. In this experiment, the oestrogenic implant appeared to have a stimulatory effect on in vitro estimates of lipogenesis.

Growth performance and body composition differences between Large White control (C) and index-selected (S) pigs were evaluated on feeding scales calculated to give very low, low and medium daily growth rates of approximately 450 g, 550 g and 650 g respectively. Starting at 30·3 (s.e. 0·32) kg, 72 boars were penned in groups of six, and one C and one S boar was fed on each of the three feeding scales for 84 days. The feeding scales started at 1·1, 1·2 and 1·3 kg per pig per day for the intended very low, low and medium growth rates with weekly increments of 0·025, 0·050 and 0·075 kg per pig per day. The 34 C and 35 S boars which completed the trial were slaughtered, their carcasses dissected and the whole empty bodies minced and chemically analysed. In no case was the interaction between line of pig and feeding treatment significant. S boars grew faster than C boars on all three levels of feeding. S boars also grew lean tissue faster, deposited less total fat, and had smaller backfat depths than C boars. Similar differences between lines in chemical composition were also apparent for whole body crude protein and lipid. Although the index selection at Newcastle was based on ad libitum performance tests, improvements in the lean content and lean tissue growth rates of the selection line were apparent even at very low levels of feeding.

Two groups of suckling Charolais cows were fed at different levels of nutrition from 70 days before the estimated date of calving until 45 days after calving, to study the effects of reduced dietary intake on pre-partum plasma levels of progesterone and total oestrogens (conjugated + unconjugated) and post-partum plasma levels of luteinizing hormone and follicle stimulating hormone. Eight control cows received a ration containing the Institut National de la Recherche Agronomique's recommendations for all nutrients, while 10 cows received a restricted diet which supplied approximately three-quarters of the recommended amounts for energy and nitrogen.

The mean weight of the two groups of cows was similar at the beginning of the experiment but the restricted group had a significantly lower weight just before calving than the control group (678 v. 766 kg; P < 0·05).

After calving, cows ont he low diet had a weight loss of 600 g/day, while those on the control diet gained 300 g/day. During the last 45 days of pregnancy underfeeding did not significantly affect oestrogen levels, but progesterone levels increased proportionally by 0·24 (P < 0·01).

During the first 45 days of lactation underfeeding decreased the number of cows showing oestrus (0/10 v. 4/8) and significantly decreased both luteinizing hormone and follicle stimulating hormone levels at 5, 15 and 30 days post partum.

Furthermore, the correlation between mean daily gain (0 to 45 days post partum) and luteinizing hormone concentration on day 30 was highly significant (r = 0·58; P < 0·01; no. = 19). These results suggest that the delay of the first post-partum ovulation in the underfed cow is due to low gonadotropin levels.

The performance of crossbred ewes sired by Border Leicester (BL), Bluefaced Leicester (BFL) and ABRO Damline (DL) crossing sires was compared. The dams of the crossbred ewes were of three hill breeds (Scottish Blackface, Swaledale and Welsh Mountain). Contemporary comparisons were made on 18 commercial and college farms throughout England and Wales from 1977 to 1981. A total of 1 277 crossbred ewes were involved with data on up to three years' lambings per ewe, giving a total of 3 522 mating records. The analyses were by least squares, fitting constants for terminal ram breed × farm × year of birth of ewe groups, sire breed, dam breed, age of crossbred ewe and all two-way interactions.

The DL crossbred ewes were lighter at mating than the other crossbreds at each age. The proportion of 1-year-old crossbred ewes lambing was highest for the DL (0·78), compared to BFL (0·73) and BL (0·62), indicating earlier sexual maturity. Over all ages, the DL crossbreds were more prolific with 1·79 lambs per ewe lambing compared to BFL (1·63) and BL (1·53) and more lambs were weaned (1·33, 1·29 and 1·19 respectively). The total litter weight at both birth and weaning of the DL crossbreds was greater than the BL crossbreds but less than the BFL crossbreds at each age. For prolificacy and early sexual maturity, the DL cross is superior to both breeds. In overall production, the DL cross had no advantage over the BFL cross, as the litters of the DL crossbred ewes were lighter than the BFL litters at both birth and 10 weeks of age

A growth trial lasting 84 days and digestibility trials were carried out with Hereford × Friesian steers weighing initially 360 kg. Daily dry-matter intakes (kg) of 32 steers offered turnips with blood meal (250 g/day) and straw treated with sodium hydroxide (SP), urea (UP), ammonia (AP) or untreated (CP), and of a further eight steers offered turnips and ammonia-treated straw without a supplement of blood meal (A) were 6·5 (SP), 6·0 (UP), 6·6 (AP), 5·9 (CP) and 6·3 (A); live-weight gains (kg/day) were 0·69, 0·58, 0·60, 0·37 and 0·39 respectively. The non-protein nitrogen intake of steers on treatments SP and CP were matched to those on treatments AP, A and UP by the addition of urea. Coefficients of apparent straw organic matter digestibility were 0·629 (SP), 0·531 (UP), 0·578 (AP), 0·446 (CP) and 0·569 (A). Overall food intakes on all treatments were low initially (88 g/kg W0·73) and declined further to 78 g/kg W0·73. Live-weight gains also were low; those of steers given diets CP and A were lower (P< 0·001) than gains of steers on other treatments.

Improvements in the apparent digestibility of straw were obtained by chemical treatment but all values, except that of the UP group, were low. The supplementation of ammonia-treated straw with blood meal (AP) produced a higher (P < 0·001) growth rate in steers compared with that of steers receiving ammonia-treated straw alone (A). The low mean pH (6·48) and ammonia concentration (9 mg/100 ml) of rumen liquor sampled during the growth trial suggest that the poor growth rates and low food intake of cattle in this trial may be associated with the rapid release of soluble sugars from turnips given only once daily.