Rate Of Live-weight Gain Research Articles

An estimate of the nutrients utilized for live-weight gain by Merino sheep.

1. One hundred and seven fine-wool Merino wethers and non-pregnant ewes varying in age from newly born to 110 months and in live weight from 1.7 to 55.1 kg were slaughtered and minced.2. The nitrogen, fat, ash, calcium, phosphorus, sodium and potassium contents of the mince were determined. Energy content was estimated from the contents of fat and fat-free organic matter.3. Weighted regression relationships were calculated between the energy, N, Ca, P, Na and K contents of the sheep, and age, live weight and (age x live weight). The relationships were differentiated with respect to age and live weight, and the rates of nutrient deposition at different rates of live-weight gain, and for sheep differing in age and live weight were calculated.4. The rates of nutrient deposition were compared with those estimated by the Agricultural Research Council (1965) and by Mitchell (1962). and were in general lower in energy content and higher in ash constituents per unit live-weight gain.

A nutritional evaluation of diets containing meat meal for growing pigs. 1. The effect of calcium level in wheat-animal protein diets

Diets containing 1.4, 2.5, and 3.5 per cent calcium were fed to pigs in two experiments to observe the effect on performance of calcium level in diets containing animal protein supplements. Rate of liveweight gain and efficiency of food conversion were depressed as the level of calcium increased. There was also a trend towards a decrease in the lean content of the ham with increased calcium intake. Dry matter and organic matter digestibility of the diets were depressed as calcium intake increased, but no apparent effect on nitrogen retention was detected. There was no indication of parakeratosis in any of the animals.

The partial and total replacement of wheat and soybean meal by pollard in a wheat-soybean meal grower-pig ration

This experiment was designed to investigate the effect of high levels of pollard in the ration on the growth and carcase quality of growing pigs. Twenty-four gilts and twenty-four male castrate weaner pigs of mean liveweight 23.4 kg were each fed one of four rations in a wet form in individual stalls twice daily until they were slaughtered at a mean liveweight of 86.5 kg. The control ration was 81.9 per cent wheat and 15.0 per cent soybean meal, with added minerals and vitamins. In the other three rations, the wheat and soybean meal portion was replaced by 48.4, 67.8, and 96.9 per cent pollard. Feed allowance was adjusted to give a similar intake of digestible energy for all rations. There was no significant difference between treatments in rate of liveweight gain or in efficiency of utilization of digestible energy. Efficiency of utilization of air-dry feed decreased as level of pollard in the ration increased. These differences were significant except for the difference between the rations containing 48.4 and 67.8 per cent pollard. There was a significant decrease in dressing percentage with each increase in the level of pollard in the ration. Backfat thickness was significantly less in pigs fed rations containing 67.8 and 96.9 per cent pollard than in pigs fed the other two rations. Gilts grew more rapidly, utilized feed and digestible energy more efficiently and produced carcases with greater eye muscle indices and higher appraisal scores than the male castrates. There were no digestive disturbances on any of the rations and all were readily eaten. The results indicate that the relationship between protein quality k d net energy in pollard is of an order normally occurring in well-balanced rations.

Beef production from nitrogen fertilized pangola grass (Digitaria decumbens) on the coastal lowlands of southern Queensland

Animal production from pangola grass (Digitaria decumbens) fertilized with 400 and 800 lb nitrogen an acre a year was measured over a two-year period 1965-1967. The nitrogen was applied as calcium ammonium nitrate (20.5 per cent N) in split applications. These were 27.5 per cent of the total in September, December, and February, and 17.5 per cent in April. The experiment was grazed with yearling Hereford heifers on a 'put and take' system at a mean stocking rate of three beasts an acre. A mean annual production of 1139 and 1215 lb an acre was obtained from 400 and 800 lb N applications respectively. Although there was 20-30 per cent greater dry matter production containing approximately 3.5 per cent more crude protein from the higher nitrogen application for most periods of the year, this had little effect on total animal production. The highest rates of liveweight gain were recorded in the period September-December, coincident with the highest crude protein and phosphate levels in plant material. Liveweight losses occurred in winter but were reduced by 50 per cent under the higher rate of nitrogen application. The results of this experiment clearly demonstrate that high levels of animal production can be obtained from pangola grass in a subtropical environment with adequate nitrogen fertilizer, even though marked seasonal differences in growth rate of the grass occur.

The effect of rate of gain during the growing and finishing periods on the feed efficiency and carcass composition of the pig: II. Contrasting patterns of growth produced by different rates of gain from 20 to 55 kg and 55 to 87 kg live weight

SUMMARYPigs were grown at controlled rates of live-weight gain from 20 to 55 kg and from 55 to 87 kg live weight, at which weight they were slaughtered. Six growth-rate treatments were compared and were referred to as High-High (HH), High-Moderate (HM), High-Low (HL), Moderate-High (MH), Moderate-Moderate (MM) and Low-High (LH). The right-hand side of each carcass was divided into the four primary jointsand each joint was physically dissected into bone, skin, subcutaneous fat and lean meat. The boneless tissue of each joint was analyzed for moisture, ether extractable fat and nitrogen.It was found that an increase in the rate of live-weight gain in the first growth period, tended toimprove the efficiency with which feed was converted into live weight. In the second growth period the efficiency of feed conversion was dependent on the rate of gain both in that period and in the preceding period. Restricted growth in the first period improved the efficiency of feed conversion both in the second period and over the entire experimental period compared with rapid early growth. The implications of compensatory growth are discussed.There was no treatment effect on carcass length, but hindleg length and ham circumference measurements showed that the proportion of gammon in the side was lower in the HH pigs compared with the other five treatments. This was confirmed by the weight of the gammon joint expressed as a percentage of the trimmed side. There was also a decrease in the proportion of shoulder and an increase in the proportion of middle in the HH pigs. Differences between the other five treatments were small. The changes in conformation were due largely to the effect on fat distribution throughout the side particularly in the gammon and back regions.The HH treatment resulted in a significant increase in the percentage fat in the side compared witheach of the other five treatments. Within these five treatments there was no significant difference in the percentage fat in the side. This suggests that equal importance may be attached to the rate of live-weight gain in both the growing (20–55 kg) and finishing (55–87 kg) periods in determining the fatnessof the bacon weight carcass.The treatments had little effect on the chemical composition of the fat-free boneless meat.The results are discussed in relation to current growth theory.

The effect of rate of gain during the growing and finishing periods on the feed efficiency and carcass composition of the pig: I. Rate of gain during the growing period from 18 to 57 kg live weight

SUMMARYTwo experiments were carried out in which pigs were grown at controlled high, moderate or low growth rates from 18 kg to slaughter at 57 kg live weight. Linear measurements and density determinations were carried out on the carcasses. In the second experiment the right-hand side of each carcass was divided into four joints and each joint was physically dissected into three components, bone, subcutaneous fat plus skin and ‘lean’ meat. The boneless tissue of each joint was analysed for moisture, ether extractable fat and nitrogen.It was found that an increase in the rate of live-weight gain tended to improve the efficiency with which feed was converted into live weight.The percentage of fat in the side was significantly increased by more rapid growth rates.The conformation of the side was altered by treatment, the proportion by weight of the middle region increased with increasing rate of live-weight gain and was accompanied by corresponding reductions in the proportions of the gammon and shoulder regions. These changes were largely due to an effect on the distribution of fat throughout the side, but there were also minor changes in the distributions of bone and fat-free lean.The high rate of gain was associated with a greater proportion of belly in the side. This was due to an increase in the proportion of lean meat in this region, presumably a functional effect caused by an increased intestinal volume.There was no treatment effect on the chemical composition of the fat-free boneless meat which was found to differ significantly between joints.

Comparison of the weight gain and the composition of blood and saliva in sheep grazing timothy and ryegrass swards.

1. After a preliminary period of 2 weeks indoor feeding on hay, two groups of wethers grazed either a timothy pasture or a ryegrass-dominant pasture for 12 weeks. The timothy was particularly low in sodium and chlorine.2. Within a week of turning out, saliva sodium fell and potassium increased in the timothy group, and by the end of the experiment, the sodium: potassium ratio was 1.9:1. The changes in saliva were not reflected in blood composition. The rate of live-weight gain was similar in both groups of sheep.3. The results confirm those of a previous indoor experiment and show that timothy supplies insufficient sodium to maintain the normal saliva composition of sheep.

Intensive beef production. 9. A note on the performance of Friesian and Ayrshire steers fattened on a cereal diet

In parts of the United Kingdom, considerable numbers of Ayrshire bull calves are slaughtered at birth or shortly after. These animals, if fattened intensively on a cereal diet, could provide a valuable addition to the beef produced from the dairy herd if their rate of live-weight gain, carcass composition and feed conversion efficiency provided an economic return. At the prevailing purchase price of calves and cost of feed the profit margin would appear to compare favourably with that from other dairy steers. The data from an economic survey of barley beef units in the North of Scotland by Clark (1966) show, on the basis of surplus per head (i.e. gross margin less other costs) that the greatest margin was achieved by a unit whose livestock was entirely comprised of Ayrshire steers.

Environmental and managerial factors affecting the growth of Friesian heifers from six months of age to calving

SummaryThe growth of 120 Friesian heifers born into one herd over a period of 12 years was studied for the period from 6 months of age to calving at about 30–35 months of age. Live weights were recorded weekly and rates of live-weight gain were calculated for each 3-month period for each animal. Δt 6, 12, 18, and 24 months of age the heifers weighed 360, 590, 800 and 950 lb. The coefficients of variation of live weight did not vary with age and averaged ±10·0%. Coefficients of variation of live-weight gain increased from ± 20% at 6–9 months of age to ±60% at 24–27 months of age. Growth rate declined by 0·02 lb/day from 12 months to 30 months of age for animals under constant managerial conditions. Heifers wintered indoors grew faster than those wintered outdoors. The growth of younger animals was decreased more by outdoor wintering (a reduction of 0·6 lb/day at 15 months) than was the growth rate of older animals (a reduction of 0·3 lb/day at 21 months of age). When live-weight gain was low in winter there was marked compensatory growth at grass the following summer. Pregnant heifers grew 0·1 lb/day faster in early pregnancy and 0·6 lb/day faster in the last 4 months of pregnancy than did barren heifers.There was no appreciable difference between the live-weight gain of spring- and autumn-born heifers. With an autumn calving policy spring-born heifers were served and conceived 135 days earlier and weighed 106 lb less at calving than did autumn-born heifers. There was little difference in the milk yield of the two groups in 305 days of the first lactation.The regression equation of live weight (lb) on age (months) to 3rd calving was W = 1449 – 2027 e-0·042t. It was concluded that in the interests of economic rearing the dairy farmer could with advantage exercise greater control of the relationship between nutrition and growth during high cost winter periods and low cost summer periods.

Castration experiments with Yugoslav Simmental cattle. I. The effect of castration on growth and live-weight gains

1. Bulls and steers of the Yugoslav Simmental breed (38 in total) were reared and fattened to 470 kg live weight. Half received a moderate level of feeding to 8 months of age and half a high level of feeding over this period; all were fed on a high level from 8 months to slaughter, their diet involving a concentrate mixture, lucerne hay and maize silage.2. At slaughter weight, steers were 2·5% higher at withers than bulls, but other body measurements showed no significant difference.3. Castrates needed a 3 to 8% longer fattening period depending on the feeding treatment.4. Castration reduced the rate of live-weight gain by 4·9% over the whole rearing and fattening period, and by 8·0% over the fattening period only.5. Bulls had better feed conversion ratios overall. Steers consumed more starch units per kg of live-weight gain—8·1% more over the whole rearing and fattening period and 9·8% over the fattening period. Consumption of digestible crude protein was also higher in steers.6. The detrimental effect of castration was more strongly expressed on the HH feeding treatment. An increase in the concentration of the rations did not improve food conversion ratios.

The Continuous Feeding of Two Antibiotics to Growing Rabbits

The effects of feeding (a) Oxytetracycline hydrochloride and (b) Chlortetracycline hydrochloride to rabbits at levels of 5, 10 and 20 mg./ lb. of food for 6 weeks on the growth rate and liver, stomach, small intestine and caecum development were studied. No significant results were obtained at the 5 mg. levels. At the 10 mg. levels there was a significant increase in the rate of live-weight gain and a significant decrease in the average weight of the caecum expressed as a percentage of the bodyweight in the case of Oxytetracycline and no significant differences in the case of Chlortetracycline. At the 20 mg. levels there were significant decreases in the percentage caecum weights with both antibiotics and in the average weights of 1 cm. lengths of small intestine and caecum in the case of Oxytetracycline and in the percentage small intestine weights with Chlortetracycline. Des suppléments de hydrochlorate d’Oxytétracycline et de hydrochlorate de Chlortetracycline ont été administrés à des lapins, pendant six semaines, aux niveaux suivants: 5, 10 et 20 mg./lb. de nourriture. Leurs effets sur la croissance des lapins et sur le développement du foie, de l’estomac, de l’intestin grêle et du caecum ont été étudiés. Aucun résultat significatif n’a été obtenu au niveau de 5 mg. Au niveau de 10 mg. on a observé une hausse significative de la courbe de gain du poids corporel et une baisse significative du poids moyen du caecum, exprimé comme pourcentage du poids corporel en cas de l’oxytétracycline, mais les différences n’ont été pas significatives en ce qui concerne la chlortétracycline. Au niveau de 20 mg. tous les deux antibiotiques ont provoqué des augmentations significatives des poids des caecums et des poids moyens de pièces d’intestin grêle et de caecum de la longueur de 1 cm. dans le cas de l’oxytétracycline, et dans les pourcentages de l’intestin grêle dans le cas de la chlortétracycline. Der Effekt der Fütterung von (a) Oxytetracyclin-hydrochlorid (OTC) und (b) Chlortetracyclin-hydrochlorid (CTC), die sechs Wochen lang in Konzentrationen von 5, 10 und 20 mg./kg. Futter an Kaninchen verabreicht wurden, wurde auf Wachstumszunahme und Leber-, Magen-, Dünndarm-und Blinddarmentwicklung geprüft. Bei 5 mg. Konzentrationen wurden keine bemerkenswerten Resultate gesehen. Bei 10 mg. Konzentrationen gab es eine bemerkenswerte Wachstumszunahme und eine bemerkenswerte Abnahme des durchschnittlichen Blinddarmgewichtes (als Prozent des Körpergewichtes ausgedrückt) bei OCT und keine bemerkenswerten Unterschiede bei CTC. Bei 20 mg. Konzentrationen gab es bei beiden Antibioticas eine bemerkenswerte Abnahme des relativen Blinddarmgewichtes, bei OTC gab es eine bemerkenswerte Abnahme des durchschnittlichen Gewichtes 1 cm. langer Portionen des Dünndarmes und des Blinddarmes und bei CTC eine bemerkenswerte Abnahme des relativen Dünndarmgewichtes. Se han estudiado los efectos de suplementos de hydroclorato de oxytetraciclina y hidroclorato de clortretraciclina a los niveles de 5, 10 y 20 mg./lb. de alimento durante seis semanas sobre el crecimento de conejos y el desenvolvimiento del estómago, del intestino delgado y del ciego. El nivel de 5 mg. no dió resultados significativos. El nivel de 10 mg. ha producido un aumento significativo del peso corporal y una disminución significativa del peso promedio del ciego interpretado como porcentaje del peso corporal en el caso de la oxytetraciclina y ninguna diferencia significativa en el caso de la clortetraciclina. Al nivel de 20 mg. se observaron disminuciones significativas en los porcentajes de los pesos de los ciegos con ambos los antibióticos y en los pesos promedios de larguras de 1 cm. de intestino delgado y ciego en el caso de la oxytetraciclina y en los porcentajes de pesos del intestino delagdo en el caso de la clortetraciclina.

The effect of inbreeding on feed consumption and utilisation by sheep

Twelve inbred (coefficient of inbreeding 25%) and 12 outbred, singlereared, Scottish Blackface castrated male lambs were taken at six months of age from amongst the progeny of three rams. They were housed and fed individually on a pelleted diet in three separate phases. In the first two phases restricted amounts were offered. These were calculated to produce, firstly, a small rate of live-weight gain and, secondly, a small rate of live-weight loss. In the third phase feed was offered to maximum voluntary intake during 2 two-hour periods daily.On restricted intakes there were no significant differences between the groups. In the third phase the outbred sheep consumed 17% more feed than the inbred group and the daily rates of live-weight gain and wool growth were 33% and 27% higher, respectively. Since the inbred lambs were smaller, the voluntary intake per unit live-weight did not differ significantly between groups.The estimated requirements of feed for maintenance (20·1 ± 0·4 and 21·9±0·6 g./kg. live-weight, respectively, for the outbred and inbred groups) differed significantly. There were no apparent differences in the estimated efficiency of conversion of available surplus feed to body tissue or wool growth.

A note on goitre in lambs grazing rape (Brassica napus)

Forage crops of the genus Brassica are known to contain goitrogens which under certain conditions can cause severe incidences of neonatal mortality in lambs and goitre in older sheep (Shand, 1952; Sinclair and Andrews, 1958, 1959, 1961; Andrews and Sinclair, 1962).In the course of studies of certain aspects of lamb growth it was noted that lambs grazing rape (Brassica napus) had heavier thyroid glands than comparable lambs grazing grass. Pipes, Premachandra and Turner (1958) found that a degree of hypothyroidism increased the rate of fattening and influenced the carcass quality of cattle, and in view of this and other evidence it was decided to test the hypothesis that changes in the weight of the thyroid glands of lambs grazing rape were associated with changes in the rate of live-weight gain.

The effect of the addition of large amounts of cod-liver oil to the rations of yearling heifers on their rate of live-weight gain

1. Groups of twenty-four heifers were used in three experiments lasting 51–98 days. The effect on rate of live-weight gain of the addition of 150 ml. cod-liver oil to the daily ration was studied.2. The same treatments were used in each experiment: a basal diet consisting of hay and concentrates and two experimental diets consisting of the basal diet plus (a) 3 lb. concentrates, (b) 150 ml. (0·30 lb.) cod-liver oil. In one experiment flaked maize was used in the concentrates in place of crushed barley.

The feed intake of milk cows I. Intake of winter rations during pregnancy and lactation and the influence of change to pasture

SUMMARY1. For 4 weeks before calving in December or January a group of 7 Ayrshire cows each received daily 6 lb. hay and silage to appetite, whilst a second group of 9 received the same roughages and 6–10 lb. concentrates. After calving, cows from both of the pre-calving treatments were placed in each of two post-calving groups of 8 cows. A High treatment received approximately 8 lb./day more concentrates at the same milk yield than the Low treatment. Both groups continued to receive 6 lb. hay/cow/day and silage to appetite. The cows were allowed to graze by day from 21 February and by day and night from 13 April. Hay, at 5 lb./cow/day and reducing rates of concentrates were offered until 8 May.2. Individual feed intakes were estimated from faecal output and digestibility. Direct measures of the intakes of different treatment groups on indoor feeding agreed fairly closely with the mean individual estimates.3. The digestible organic matter intake (DOMI) of 1,300 lb. cows in the last stages of pregnancy was increased from 10 up to 14–16 lb./day by giving 8–10 lb./day concentrates. Immediately after calving, the increases in DOMI compared with pre-calving levels were about 2.5 lb./day for cows which received concentrates before calving and 8.5 lb./day for cows which received no concentrates before calving.4. When all cows had calved and were in full milk production there were no significant differences in DOMI, milk yield or rate of live-weight gain attributable to pre-calving treatment. Mean DOMI on the High and Low post-calving treatments were 23.8 and 19.4 lb./day, mean fat-corrected milk yields 44.5 and 38.8 lb./day and mean rates of live-weight gain 05 and nil lb./day, respectively.5. DOMI increased by 0.7 and 4.9 lb./day for High and Low post-calving treatments when cows were turned out to night as well as day grazing, and milk yields increased by 1.0 and 2.2 lb./day respectively.6. Regression equations relating animal production and feed intake, and substitution rates of concentrate usage were calculated. Faecal output and DOMI were closely related to milk yield. When additional concentrates were given the resulting increase in total DOMI was greater when the bulk feed was of low digestibility than when it was of high digestibility.

Protein and energy nutrition of the bacon pig. II. The effect of varying the protein and energy levels in diets of ‘finishing’ pigs

1. A feeding trial has been carried out with sixty-four individually fed Large White pigs offered eight different diets prepared at four energy levels and two levels of crude protein. A record was maintained of the rate of live-weight gain and food was given at a defined restricted level. Carcass quality was assessed by a procedure of complete dissection into visible fat, lean, etc.2. Though differences in the rates of live-weight gain and food conversion efficiency were not statistically significant, the best performance was recorded when the diets contained 16 % crude protein and yielded the equivalent of 2950 kcal. digestible energy per kg. upon oxidation. The energy: lysine ratio (kcal. digestible energy per kg. per unit percentage lysine in the ration) was approximately 3500.

Implantation of oestrogenic hormones in Beef Cattle

Abstract The carcasses of 24 Aberdeen Angus steers were obtained from an experiment examining the effects of implantation with oestradiol benzoate plus progesterone on rate of liveweight gain. There were eight animals in each of three groups (control, autumn-, and springimplanted). Bone-in carcass conformation was assessed by two methods of jointing, by carcass measurements and quality scores, and by derivation of a carcass wholesale value Index in pence/lb. Implanted animals, which made faster weight gain than controls, produced heavier carcasses. Weights of individual cuts tended to increase proportionately with carcass weight. Adjusted for carcass weight, controls yielded more Kidney and Channel Fat than implanted, and autumn- more than spring-implantation. Group differences were also evident for combinations of“Good Cuts”, and carcass measurements revealed only that controls were fatter, and heavier in relation to their length, than the carcasses of implanted steers. Carcasses from controls were of less total monetary value than those from implanted steers. The highest return/lb of carcass (wholesale value Index) resulted from spring-implantation. This Index was not associated with any of the recorded carcass measurements, nor with carcass scores. Prediction of the Index from individual and groups of cuts was examined and it was concluded that a grouping of relatively high-priced cuts could be used to estimate value/lb.

THE USE OF GRAZING CONTROL FOR INTENSIVE FAT‐LAMB PRODUCTION

The effects of three stocking rates on fat‐lamb production were examined. These stocking rates were imposed upon four grazing systems. The grazing managements had no significant1 effects upon the rate of liveweight gain or the total liveweight of lamb produced per acre, nor were the ewes’ liveweights significantly affected. Reasons are suggested. The lambs’ rate of liveweight gain was related negatively and the total liveweight of lamb produced per acre was related positively to stocking rate. The ewes’ liveweights were similarly affected, there being the highest losses of liveweight under the high stocking rate. In all cases significant differences existed between the stocking rates and there was a significant linear relationship between them. It is concluded that high stocking rates are essential to obtain the maximum fat‐lamb production on a ‘per acre’ basis.

THE FEEDING VALUE OF DRIED POTATO PULP FOR PIGS

Dried potato pulp (molassed) was fed to growing pigs to replace barley and to finishing pigs to replace oats in the rations. Levels of 0, 15, 30 and 45 per cent potato pulp, in place of barley, were tested with pigs from weaning to market weight. Although 22 per cent potato pulp in a growing ration reduced (P < 0.05) the rate of liveweight gain, results indicated that up to 15 per cent potato pulp allowed satisfactory gains.The replacement of oats by potato pulp in a finisher ration gave an increased rate of gain which was not statistically significant. A level of 30 per cent potato pulp in growing-finishing rations gave lower (P < 0.01 and 0.05 respectively) rates of gain than did the zero and 15 per cent level. Feed efficiency was reduced significantly by all levels of potato pulp fed through the growing-finishing period. Potato pulp appeared to influence "fill" as reflected in lower dressing percentages based on liveweight at marketing. Compared with the controls, 45 per cent potato pulp reduced (P < 0.05) depth of shoulder and loin fat. Coefficients of apparent digestibility for potato pulp dry matter, crude fiber and energy were 81, 75, and 76 per cent respectively; but the crude protein, approximately 7 per cent of the dry matter, was only 25 per cent digestible. This finding emphasized the need for protein supplementation of pig rations containing potato pulp.

A comparison of growth rate in twin cattle of eight breeds and crosses

SUMMARY1. Rates of live-weight gain from 2 to 96 weeks of age are compared in twin cattle of 8 breeds and crosses. The 258 animals in the trial consisted of 77 pairs of one-egg (MZ) and 52 pairs of two-egg (DZ) twins. All were females.2. Between collection during the first week after birth, and 36 weeks of age, treatment of animals was uniform. After this some animals were grazed and others remained housed, depending on their date of birth. Members of each twin pair were, however, always treated alike. Between 36 and 96 weeks of age grazed stock gained 62 lb. more weight than housed stock. This difference was allowed for in making breed comparisons.3. The trial period was divided into six stages. The most rapid gains were made between 24 and 36 weeks of age (1·43 lb. per day) and between 36 and 52 weeks (1·48 lb. per day). Earlier and later growth rates were about 30% less than these.4. Rates of gain varied from 1·10 lb. per day in Ayrshires to 1·38 lb. per day in Friesian × Shorthorn crosses. The Friesian and its crosses with Shorthorn generally made fastest gains throughout the trial. The Ayrshire was slower than the rest. The Shorthorn and its crosses with Hereford and Ayrshire were intermediate in performance.5. Ratios of within-pair variance in MZ and DZ twins indicate that differences in performance are most strongly dependent on genetic differences-at 12 to 24 and 52 to 72 weeks of age.