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.

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

GENETICALLY STANDARDIZED GROWTH EQUATIONS

St C. S. Taylor

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.

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 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.

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.

1. The digestible energy content of 14 meat meals and meat and bone meals produced from different regions in eastern Australia was determined using growing pigs. The relationship between digestible energy content and chemical constituents in the meals was investigated.

2. Digestible energy ranged from 9·4 to 13·9MJ/kg (air-dry basis). This variation in digestible energy was best described by the regression equation:

3. Simpler equations, with only gross energy or crude protein and ether extract were:

4. Digestibility of the energy and crude protein in the meals ranged from 0·63 to 0·77 and 0·73 to 0·91 respectively. These variations were not related to any of the major chemical constituents of the meals.

Four diets which varied in crude protein concentration from 140 to 240 g crude protein per kg dry matter were given to gilts in experiment 1, and two diets containing 140 and 200 g crude protein per kg dry matter were given t o boars and barrows in experiment 2. Two levels of feeding were offered in both experiments and energy and nitrogen balances were measured at 30 and 90 kg live weight in both experiments, and also at 50 kg in experiment 1. Nitrogen intake had a small negative influence on energy retention by pigs of all sexes, an effect which was independent of the large positive effect of metabolizable energy intake. The ratio of metabolizable energy concentration to digestible energy concentration decreased in association with increases in crude protein concentration of the diets. The results show that comparisons of feeds on the basis of their digestible energy concentrations would lead to overestimation of the energy values of those containing high protein concentrations. Live weight (or age) and metabolizable energy intake exerted positive influences on the amount of energy retained per kg live-weight gain, whereas nitrogen intake exerted a negative influence. Values for energy retained per kg live-weight gain predicted from multiple regression equations, together with calculated values for maintenance and net efficiency, were used to predict the energy retention and growth rate of pigs in various circumstances.

Nitrogen retention increased in association with increases in nitrogen intake for pigs of all sexes at 30 kg live weight; there was also a corresponding increase for boars at 90kg live weight, but not for gilts or barrows at this weight. Boars retained more nitrogen than did barrows at 30 and 90 kg live weight only if given the diet with the higher concentration of protein.

Metabolizable energy intake appeared to exert a small positive influence on the nitrogen retention by pigs of all sexes at 90kg live weight; however, it appeared to have no influence on nitrogen retention by pigs at 30kg live weight.

Attainment of puberty and the ovulation rates for the first three oestrous cycles were studied in gilts reared to 160 days alongside contemporary castrate or entire males before introducing them to mature boars.

Gilts which were introduced to the boars at 160 days of age reached puberty at younger ages and lighter weights than isolated gilts. Rearing treatment did not affect the age of puberty. Gilts which were isolated from boars after 160 days of age reached puberty earlier if they had been reared with entire rather than castrate contemporary males. The interval from introduction of the boars to first oestrus was related to age and weight at the time of introduction.

Ovulation rate at the pubertal oestrus was the same in both isolated groups, and higher in both these groups than for gilts induced into early puberty by boars. Ovulation rate increased at the second and third oestrous cycle and groups differed only at the first oestrus. In a second experiment, the reproductive performance of gilts approximately 218 days of age experiencing either their first, second or third oestrus was studied. No differences were found among the groups and the conclusion is that in gilts of similar age and weight the oestrous cycle at which mating takes place does not affect reproductive performance.

Fifty-one ewes with single lambs and 87 ewes suckling twin lambs (mean ewe live weight, 67 kg) were given a basal diet of 1·0kg hay and 1·0kg whole oats, providing approximately 16·7MJ metabolizable energy and lOOg digestible crude protein per day. Three supplements (A, B and C), providing an additional 45 g digestible crude protein, were compared. Supplement A consisted of 40 g of a fully-soluble liquid product (LS) containing urea, (equivalent to 1090g crude protein per kg), minerals and vitamins; B was 16g urea with solid minerals and vitamins; and C was 125g soya bean meal given in substitution for the same amount of whole oats plus solid minerals and vitamins. The growth rate to 6 weeks for single lambs (11 kg) was unaffected by treatment. For twin lambs the growth rates were 7·5kg (LS), 7·1kg (crystalline urea), 7·8kg (soya) and 6·4k g (unsupplemented) (s.e. of mean = 0·31 kg). Ewes with twin lambs given crystalline urea or LS lost more live weight (approximately 1·04kg) than those given soya (6·6kg) over the first 6 weeks of lactation. The maintenance of normal concentrations of calcium and phosphorus in the blood of ewes suggested that the low total intakes of approximately 4·1 g calcium and 4·7 g phosphorus by the ewes were not inadequate.

Records were available for the progeny of Dorset Down, Oxford, Suffolk, Ile-de-France, Oldenburg and Texel sires out of Border Leicester × Blackface and Animal Breeding Research Organisation Dam Line × Blackface ewes. The data analysed were: (a) growth traits to 12 weeks for 2585 lambs, the progeny of 102 sires; (b) growth traits for slaughter at fixed weights of 35kg and 40kg for 1884 lambs (79 sires); and (c) half carcass dissection traits for 956 lambs (65 sires).

Oxford and Suffolk cross lambs were heaviest at all ages and thus youngest at slaughter. Texel cross lambs grew slowly to 12 weeks but were not significantly older than Dorset Down, Ile-de-France and Oldenburg cross lambs at slaughter. The Texel cross produced the leanest carcass with a high lean/bone ratio and eye-muscle area. Dorset Down and Ile-de-France cross lambs were fattest at slaughter but had high values for lean/bone ratio and eye-muscle area. Interactions between breed of sire and slaughter weight were non-significant for all traits (P>0·05).

Breed differences in carcass composition were also compared statistically as if at a constant percentage of subcutaneous fat. The differences were not so great as at constant live weight but the Texel cross would have had the leanest carcass. Side weights would be heaviest in the Texel and lowest in the Dorset Down and Ile-de-France. Oxford, Suffolk and Dorset Down cross lambs would be youngest at slaughter and Texel and Oldenburg crosses oldest.

Fat thickness and measurements of the m. longissimus (‘eye’ muscle) were taken at the last rib in 350 lambs' carcasses which were fully dissected. The lambs were from two ewe breeds, Clun and Colbred, and two ram breeds, Suffolk and Hampshire, and the carcass weight range was 15 to 21kg. Castrated males and females, and singles and twins, were evenly represented.

Rib fat thickness (J) was a slightly more precise predictor of the weights of lean, subcutaneous fat and subcutaneous plus intermuscular fat, when used in a multiple regression equation along with carcass weight, than fat thickness directly above the greatest depth of the ‘eye’ muscle (C). Both of these were more precise predictors than ‘eye’ muscle width and depth. Accounting for breed, either by allowing for different intercepts or completely different regression lines, did increase the proportion of variation in tissue weights explained by carcass weight and J or C, but to a small and, it was considered, commercially unimportant extent. This was despite differences in conformation between the breeds, reflected in this work by smaller ‘eye’ muscles in the ewe than the ram breeds and also in maturity, which might have been expected to influence tissue, including fat, distribution.

The results indicate that breed differences in partition and distribution within and between the carcass fat depots in sheep are smaller than those between the carcass and intra-abdominal fat depots.

A feeding trial was carried out, using 180 pigs, to assess the effect on performance when intact male and female pigs were housed together in the same pens from 20 to 90 kg live weight. There were no significant differences in daily feed intake, rate of growth or feed: gain ratio between pigs from mixed-sex pens and pigs from single-sex pens. Carcass measurements indicated slightly leaner carcasses for intact male pigs whether housed in separate pens or together with female pigs, while female pigs likewise had a significantly higher dressing percentage.

Two groups of crossbred ewes, produced by crossing the Scottish Blackface with two prolific sheep breeds, the East Friesian and the Animal Breeding Research Organisation Dam Line, were compared in good lowland conditions over three ages (2 to 4 years) from 1976 to 1978. The East Friesian crossbred ewes were heavier, had larger, heavier litters and had heavier lambs at weaning. More of their lambs were slaughtered directly off their dams, at heavier weights and at earlier ages. The total weight of lamb sold per ewe was about 15% higher than for the Dam Line crossbred ewes.