The inter-species relationship between mature body weight and time taken to mature in body weight was studied empirically in nine domestic species with data ranging from early embryonic to late postnatal growth. When examined in terms of genetic size scaling, the results showed that metabolic age provided a readily useable comparative age scale which would allow results obtained from one species to advance the study of growth and nutrition in other species.

A standardized growth curve was therefore calculated for each species in terms of degree of maturity in body weight and metabolic age. The two standardized regression curves gave mean growth curves that estimated expected degree of maturity at a given metabolic age and expected metabolic age at a given degree of maturity. The two mean curves scarcely differed.

Deviations of each species from these mean curves were analysed. There were significant standardized differences between species in earliness of maturing. Rabbits were estimated to mature in 30% less time than expected for their size, a deviation which (if repeatable) could be of great potential importance to animal production.

The growth of adipose tissue was investigated in lines of mice selected for high and low body weight at 5 and 10 weeks of age, by dissecting and weighing individual fat depots from mice aged 5, 7·5, 10 and 15 weeks. At fixed ages most depots were heavier in the High lines and lighter in the Low lines. Depots grew at different rates and the rate of total fat deposition relative to gain in body weight was greater in High than in Low lines. At about 20g live weight High and Low lines had similar proportions of total fat; at lower weights the High lines were relatively leaner. These correlated effects of selection were more pronounced in the faster growing depots of the kidneys and gonads. In consequence, the High an d Low lines had different fat distributions at fixed ages, at fixed body weights and at fixed weights of fat.

Changes in the frequency of the poll gene and the effect of polledness on production were measured from 1970 to 1979 in four closed lines of crossbred cattle. The lines were Africander cross (AX), Braham cross (BX) and two Hereford × Shorthorn (HS lines, one selected for production (HSS) and one a control line (HSR).

Calves were classified as horned, polled or scurred. Except in the HSS line, horned males were more common than horned females. Horned HS bulls sired only horned calves when mated to horned cows but corresponding matings of AX and BX breeds produced some polled progeny. The incidence of scurs was highest in the AX line, lowest in the HS lines and higher in males than females. These observations are discussed in relation to existing models of inheritance of horn-type.

Prior to 1970 the frequencies of the poll gene declined from their initial values in the BX and HS lines and increased in the AX line. These changes were ascribed to random genetic drift. After 1970 the frequency of the poll gene remained stable in all lines.

No significant differences were observed between horned and polled cattle in live weight, fertility or mortality rates indicating that polledness had no detrimental effect on production in these lines.

ANIMAL PRODUCTION, Volume 30, Part 2, pp. 167-175

GENETICALLY STANDARDIZED GROWTH EQUATIONS

St C. S. Taylor

Changes in progesterone levels in milk and in milk fat were measured by radioimmunoassay in nine crossbred cows for 40 days after insemination. On average, progesterone in milk was minimal: 1·10μg/l at the morning milking (M) and 1·63μg/l at the evening milking (E) on the day of oestrus; this increased to 15·72 μg/l at M and 22·8 μg/1 at E on day 13 after insemination, and thereafter declined to 0·99 μg/l at M and 1·12μg/l at E on the day that the next oestrous cycle commenced in non-pregnant cows. In pregnant animals the level was maintained, and fluctuated from 1505 to 19·60μg/l at M and 18·09 to 23·01 μ/1 at E up to 40 days of pregnancy.

The average progesterone concentration in milk fat was 18·9μg/l at M and 24·1 μl at E on the day of oestrus, and rose to a peak of 141·7μ/l at M and 153·8μg/1 at E on day 13 after insemination. It continued to increase and fluctuated between 160·6 and 195·8μg/l at M, and 161·1 and 225·6μg/l at E, in pregnant animals, but dropped to 12·0μg/1 at M and 16·7 μg/l at E on the day of the succeeding oestrus in those animals which failed to conceive. Progesterone concentration in milk and in milk fat was significantly higher in evening samples than in morning samples (P<0·05).

A study of the factors that influence the age at first oestrus has been made with 57 Friesian heifers reared on high planes of nutrition in a partially-controlled environment. Although animals born during the period of increasing daylength reached puberty approximately 2 months earlier than those born during decreasing daylength, there was also a marked influence of live weight at 182 days of age and of the phase of the moon at the time of oestrus.

Frequency of occurrence of first oestrus and of conception showed four distinct peaks at approximately 7-day intervals within the lunar cycle; this association between conception and lunar phase appeared to decline with increasing parity. Frequency of occurrence of artificial insemination, which reflected all suspected instances of oestrus, was also related to lunar phase. This effect of the lunar phase appears to be associated in the young heifer with 7-day cycles of oestrous activity positioned in time by the occurrence of the full moon.

The fibrous roughages, wheat straw (WS) and cotton stalks (CS), were left untreated or treated with 30 g sodium hydroxide per kg, and residual alkali was either neutralized with sulphuric acid or left unneutralized. All roughages were pelleted and used either in complete feeds or separately. The effects of these treatments on the nutritive value of the roughages were examined in digestibility trials in vitro and in vivo, and in a 7·month feeding trial of a factorial arrangement of 2 × 3 × 2, in which the roughages constituted 350 g/kg of the diets. Approximately 150 g/kg of the neutral-detergent fibre (cell wall) constituents of both roughages was solubilized by sodium hydroxide treatment, while the changes in acid-detergent fibre components (cellulose and lignin) were much smaller, although evident.

In vitro-dry matter digestibility of wheat straw was 22 % higher than that of cotton stalks, and its increase due to NaOH treatment was 50% and 30% for wheat straw and cotton stalks, respectively. In vivo digestibility of organic matter of wheat straw was increased from 0·47 to 0·59, and that of cotton stalks from 032 to 037. The increase was evident in all components except protein, in which digestibility was reduced. The increase in the metabolizable energy values of wheat straw from 6·86 to 7·45MJ/kg dry matter and that of cotton stalks from 4·77 to 5·10MJ/kg dry matter following sodium hydroxide treatment was not reflected in daily live-weight or carcass-weight gain in the feeding trial. The animals offered NaOH-treated roughages had significantly more fat trim, and more fat in the large depots. Including roughages in complete feeds revealed no advantage in metabolizable energy conversion into live weight.

Mean daily milk yield, fat percentage and protein percentage were recorded monthly, from August 1978 to July 1979. for 579 303 British Friesian, 6 608 Shorthorn, 27 374 Ayrshire, 19 529 Jersey, and 19 760 Guernsey cattle and classified by breed, parity and stage of lactation. Parameters of the function y(n) = anb ecn were estimated for each breed/parity group for yield, fat percentage and yield, protein percentage and yield, and energy (MJ) output as milk (b and c describe the shape of the curve, a is a scalar, n the week of lactation and e the base of natural logarithms). In the mature cows of each breed (parity 4 or more), the shape constants (b, c) for milk, fat and protein production in kg respectively were:

Generally, cows of all five breeds which calved in the winter produced about 4% more milk, fat and protein than average, and those that calved in the summer produced about 4% less. After allowing for that, and removing the effect of the calving pattern, a seasonal variation in production occurred to produce a peak in June 1979 nearly 12% above average for liquid milk, in July 1979 about 4% for fat and in June 1979 about 12% for protein production (not percentage). Trough month was January 1979 for all three characters: —8%; —4% and — 9% respectively.

A consideration of the theory of metabolizable energy suggested that the peak of energy output which occurred about week 4 of lactation in all breeds and parities, expressed as a fraction of the live weight of the animal, had a critical bearing on the need to mobilize body reserves.

The fattening process of male cattle was divided into three weight stages: 150 to 250kg, 250 to 400kg, 400 to 490kg. Seventy animals were fed either a control (C) diet containing 10·3 MJ/kg metabolizable energy and some hay, or an experimental (E) diet containing 8 4 MJ/kg, in which NaOH-treated wheat straw (450g/kg) and long straw (50 g/kg) were incorporated.

The diets were given during the three weight stages to five treatment groups as follows: 1. C-C-C. 2. E-E-E. 3. C-E-E, 4. C-E-C, and 5. E-E-C. The average daily gain and metabolizable energy conversion ratios were: 1344, 980, 1127, 1145, 1094g/day and 71·4, 90·6, 77·3, 73·7, 79·8 MJ/kg live weight, respectively. The saving of concentrates plus hay in groups 2 to 5 compared with group 1 was 1·33, 1·65, 0·84 and 0·91 kg/kg live weight respectively, and the concentrates plus hay by straw replacement ratio was 3·80, 2·12, 2·00 and 3·06, respectively. Dressing percentage and percentage of fat in the large depots of the animals in groups 1 to 5 were 57·2, 58·7, 58·3, 57·8, 57·9 and 3·88, 2·28, 2·52, 3·42, 2·81, respectively. The results suggest that it is not economical to feed the E-diet to animals before they reach a weight of 250 kg, and that termination of the feeding process by a highly concentrated diet is not advantageous.

Live weight, milk yield, fat, protein and lactose percentage of 236 cows and heifers of four breeds of dairy cattle were recorded at 2-week intervals, starting within a week after calving, during the winter and spring of 1972/73. Lactation curves of the form X(n) = Xnb ecn were fitted to each animal's records, where X, b, c are constants, e the base of natural logarithms and X(n) the value of the character at the nth 2-week interval. Correlations between the curves, and between deviations from the curves, showed that the production of milk, fat, protein and lactose was negatively correlated with live-weight change in the long term, but that deviations from the curves were not correlated. There were significant positive correlations between milk yield and size, and between potential compositional quality and size (the values of × in the model). Of the four breeds studied, Friesian, Ayrshire, Guernsey and Jersey, adult Friesian cows required less dietary energy per kg of total solids produced than any other group, according to the principles of the metabolizable energy system of calculating energy requirements. During the period of negative energy balance, an average 10% to 15% of energy output in the form of milk was derived from the mobilization of body reserves.

1. Experiment 1. Six treatment groups of one British Friesian and four South Devon × British Friesian bulls, initially 432 kg mean live weight and aged 491 days, were offered individually maize or grass silage ad libitum plus 0, 5 or 10g barley dry matter per kg live weight daily for 80 days. The silages had similar digestible dry matter and estimated metabolizable energy contents but the grass silage contained more ammonia and acetic, propionic and butyric acids. Mean values for groups receiving respectively maize and grass silage diets were for dry-matter intake 17·7, 20·3, 20·4 and 13·0, 16·6, 18·7 g/kg live weight and for live-weight gain 1·00, 1·32, 1·46 and 0·65, 0·98, 1·22kg/day. Significantly more maize than grass silage dry matter was eaten when the silages were given alone and dry-matter intakes, live-weight and carcass gains were greater for maize silage diets. Dry-matter intake, live-weight and carcass gains, efficiency of feed use and carcass quality significantly improved when barley was given.

2. Experiment 2. Six groups of five British Friesian bulls, initially 418 kg mean live weight and aged 474 days, were offered individually maize silage ad libitum with either urea or one of two quantities of aqueous ammonia mixed in at the time of feeding, plus 0 or 5 g barley dry matter per kg live weight daily for 90 days. The urea and ammonia-treated silages contained 125, 124 and 148 g crude protein per kg dry matter respectively, with pH values of 3·8, 3·9 and 4·3, and when given alone or with barley mean daily intakes (g dry matter per kg live weight) were 17·1, 18·6 for urea-treated silage diets, and 17·8, 18·8 and 16·9, 19·1 respectively for ammoniatreated silage diets. Live-weight gains were 0·69, 0·94, 0·63, 1·09, 0·64 and 1·07 kg/day. Ammonia treatment had no effect on intake or live-weight gain. Live-weight and carcass gains and carcass quality improved when barley was given.

3. The maize silage offered in Experiment 1 contained similar metabolizable energy but more starch than that in Experiment 2 and was used more efficiently for live-weight gain.

Seventy-two British Friesian cows, with a mean calving date of 21 January, were used in a 3 × 2 factorial design experiment to assess the effects of the interval between harvest and wilting on the value of grass silage for milk production. Three regrowth intervals of 5, 7 and 9 weeks were used with each material ensiled both unwilted and after wilting to a dry-matter content of approximately 450g/kg. The six silages were offered ad libitum in addition to 7·6 kg concentrates per day, from day 8 of lactation until 13 April, with a mean experimental period of 67·5 days. The mean intakes of silage dry matter were 11·2, 9·8 and 8·7 kg/day for the 5-, 7 and 9-week regrowth intervals respectively and 9·6 and 10·2kg/day for the unwilted and wilted silages respectively. Regrowth interval significantly affected milk yield with mean yields of 24·7, 24·2 and 22·5 (s.e. 047) kg/day being obtained for the 5-, 7- and 9-week intervals respectively. Wilting significantly depressed milk yield with mean yields of 24·8 and 227 (s.e. 0·39) kg/day being recorded with the unwilted and wilted materials respectively. Live weight at the end of the experiment was not significantly affected by any of the treatments but the rate of live-weight loss, calculated by linear regression over the experiment, and loss in body condition score both significantly increased with increasing regrowth interval. Wilting had no effect on live weight or body condition. Increasing the regrowth interval also significantly reduced the solids-not-fat and protein contents of the milk produced during the final week of the experiment but no other significant effects were recorded on milk composition.

Blood analysis data are presented: blood urea was the only component affected by the treatments and decreased significantly as regrowth interval increased.

1. Ground forages were digested in vitro in rumen liquor supplemented with four concentrations of magnesium as MgSO4-7H2O (5, 20, 80, 320mg Mg/1) to determine the effects of magnesium on organic matter digestibility. A medium concentration of magnesium (generally 80 mg/1) resulted in optimum digestion although there was a large interaction between forage type and the response to magnesium.

2. Supplements of MgSO4-7H2O (2g Mg/day) increased the apparent digestibility of two types of hay fed to sheep, the difference being significant for poor quality hay (P<0·05).

3. The milk production of hypomagnesaemic cows given supplementary magnesium either orally, by rectal infusion, or by subcutaneous injection was compared. Plasma magnesium concentrations were increased to a similar and significant extent (P<0·01 ) but a significant increase in milk and fat production occurred only in the orally treated cows (P<0·05).

It was concluded that a dietary magnesium deficiency results in reduced rumen fermentation and hence poor production, as well as hypomagnesaemia. It was suggested that the effects on performance of other mineral deficiencies may also be mediated in part through depressions in rumen digestion.

The performance of groups of Holstein-Friesian, Dutch-Friesian and Friesian × Africander heifers in the coastal belt of Mozambique was compared over a 3-year period. The three groups of heifers were kept together under a reasonable level of management and feeding, and measurements were made of age at first calving, milk yield, days i n production, milkability, udder wearability, mastitis incidence, calving difficulties, reproductive efficiency, disease incidence, parasitic resistance and mortality.

The highest milk production was obtained with the Holstein-Friesians followed by the Dutch-Friesians. Last came the Friesian × Africander which also showed older age at first calving, poorer milkability, fewer days in production and more udder wear. No significant differences were found in calving difficulties, disease incidence, parasitic resistance, mastitis incidence and mortality. The fertility level was relatively low in all groups.

The results corroborate reports made by several workers that acclimatized European breeds can produce milk efficiently in the not-too-harsh areas of the tropics and sub-tropics if they are properly managed and fed. The main problem seems to be the relatively low fertility rates that are common in these areas regardless of breed.

Seventy-two male castrates (60 British Friesian and 12 Lincoln Red Shorthorn × (Hereford × British Friesian)) were used. The barley was offered either once daily or in a homogenous mix (complete diet) at different proportions of the total dry matter. The diets ranged from silage alone to one of rolled barley plus 1 kg long hay per day. Animals on the complete diet had greater intakes (8·9%) than those offered their barley once daily but this was not reflected in significantly greater daily live-weight gains. Curvilinear regressions were fitted to the data but further investigations with different breeds of cattle and qualities of grass silage will be required before they can be used with any assurance for predictive purposes in advisory situations. When steers were fed on diets with more than 0·40 barley in the total dry matter their intakes declined but their calculated energy (MJ metabolizable energy) intakes remained similar. It is suggested that this finding should be taken into account when diets for cattle are formulated for advisory purposes.

In a trial of a changeover design, 12 British Friesian castrates (steers) were offered both grass silage and crushed swedes (Brassica napus) ad libitum so that they could show their preference for these feeds on a free-choice basis. Two additional dietary treatments were provided by the supplementation of either swedes or grass silage with 2 kg of rolled barley. Steers consumed 0·32 of their dry-matter intake as silage when offered a free-choice of crushed swedes and grass silage. Supplementing the diet with 2 kg of rolled barley significantly increased daily dry-matter intake but the increase was not affected by the location of the supplement, on either the silage or the roots.

Monensin increases propionic acid production in the rumen and improves the efficiency of feed conversion in fattening cattle. Trials carried out in the USA showed that 200 mg monensin/head per day was the optimum dose for increasing the rate of live-weight gain in beef cattle at pasture.

Twelve pasture trials, involving a total of 434 beef cattle, were carried out during 1976 and 1977 to assess the efficacy of monensin for grazing cattle under European conditions. Each trial compared a group given 200 mg monensin/head per day in 0·5 to 10 kg of carrier supplement with a negative control group, fed blank supplement. The average initial live-weight was 260 kg and the average trial duration was 119 days. Daily live-weight gains of the control and monensin-treated cattle averaged 0·786 and 0·893 kg/head per day respectively, an advantage of 107g/head per day or 13·7 % in favour of the monensin treatment (P<0·001). The growth-promoting effect of monensin showed no tendency to diminish with time.

1. The digestible energy content of eight samples of barley, sorghum, wheat, weather-damaged wheat and wheat by-products produced from different regions of eastern Australia was determined using growing pigs. The relationships between physical and chemical composition and digestible energy content of the meals were studied.

2. The mean and range in digestible energy (MJ/kg, air-dry basis) were, respectively: barleys 12·7 (12·4 to 13·0), sorghums 14·4 (14·1 to 14·9), wheats 14·4 (14·0 to 15·0), weather-damaged wheats 14·1 (12·9 to 14·9) and wheat by-products 12·4 (10·9 to 14·1).

3. All possible regressions of digestible energy content against density, gross energy and proximate analyses of the meals were screened to select useful relationships. These screens indicated that, with the exception of wheat by-products, the majority of variation in digestible energy was due to gross energy and fibre. For wheat by-products, a combination of density and fibre accounted for most of the variation.

4. Prediction equations had the most application to weather-damaged wheats, wheat by-products and a combination of all samples.

5. There was no indication that neutral-detegent fibre was superior to crude fibre as a predictor of digestible energy in cereals for pigs.

Six production cycles, each of 212 days' duration, were completed with Rambouillet and Suffolk ewes. One group of each breed was maintained under natural light conditions (control) and three groups of each breed were under the influence of various light treatments applied regularly in a rhythmic fashion within each production cycle. Comparison of conception rates between production cycles, breeds, and treatments showed that only in production cycle 2 (mating in June) were the conceptions in control ewes of both breeds significantly lower than those in ewes on altered light treatments. The most meaningful result was the effect of light treatments on prolificacy. Treatment 3 (106 days with 16-h light per day and 106 days with 8-h light per day) gave significantly higher prolificacy than control and treatments 1 (106 days with 8-h light per day starting 65 days before mating) and 2 (42 days with 16-h light per day, then light reduction at 21 min/week for 160 days). Rambouillet and Suffolk control ewes produced annually 179 and 174 lambs per 100 ewes exposed to rams. Corresponding productions were 200 and 197 for treatment 1, 193 and 226 for treatment 2, and 223 and 242 for treatment 3.

In a grazing experiment, the organic matter digestibility of herbage selected by sheep grazing at two stocking rates was determined at monthly intervals over a 9-month period by (i) the in vitro determination of organic matter digestibility of the material collected from sheep fitted with an oesophageal fistula, and (ii) derivation from the prediction of digestible organic matter intake with a faecal nitrogen regression. A comparison of the two techniques confirms the view of other workers that faecal nitrogen indices based on pen feeding trials of green herbage are unreliable for predicting digestibility of green herbage in the field. The bias which is produced by faecal nitrogen regression appears to be associated with the time spent grazing by the animal each day. Relating organic matter digestibility directly to nitrogen content of faeces of grazing sheep (N, g nitrogen/100 g faecal organic matter) and their grazing time (T,h) yielded the following equation:

The expression has standard errors (±2·6) similar to those involved in an in vitro determination. It provides a simple technique for estimating digestibility of herbage eaten by grazing sheep, but this may only be applicable to the particular sward conditions.

Field estimates of digestibility over summer and autumn by this equation were found to be similar to estimates by a faecal nitrogen expression established from hand feeding sheep with dry summer herbage.