Twin Heifers Research Articles

黒毛和種一卵性双子の経腟生体卵子吸引成績に及ぼす飼養方法および遺伝的要因の影響

供卵牛の飼養方法と遺伝的要因が生体卵子吸引（以下，OPU）成績に及ぼす影響を胚の切断2分離により作出した黒毛和種雌一卵性双子4組計8頭を用いて検討した．10～14ヵ月齢から双子の一方を肥育用管理（肥育区）に，他方は繁殖用管理（繁殖区）に振り分けた．各双子組の両方のウシでOPU操作が可能となった時点から肥育区のウシのOPU操作ができなくなるまで1週間間隔で継続して全8頭のOPUを行った．OPU回数は双子組により12～26回と変動したが，各組での実施回数を統一するために12回目までの成績を用いて統計処理を行った．OPU実施時の推定卵胞数は飼養方法による差はみられなかったが，双子組間に有意差が認められた．OPUによる回収卵子率では飼養方法間，双子組間とも有意差が認められ，これは飼養方法および個体による腹腔内脂肪の付着の程度がOPU操作に影響を与えたとも考えられた．回収卵子の品質には飼養方法間，双子組間の違いはみられなかった．以上より，OPU成績は，肥育牛向け管理および繁殖牛向け管理という飼養方法の違いによる影響を受けない遺伝的に決まっている卵胞数の多寡に影響を受けることが認められた．また，回収卵子率は双子組間および飼養方法間で差がみられたことから，個体による腹腔内脂肪の付着の程度を含めて，遺伝的および環境要因がOPU時の経直腸ならびに経腟での操作に影響を与えることが示唆された．

A note on consequences of single-trait selection for insulin-like growth factor 1 (IGF-1) in beef heifers

Eight sets of identical twin heifers and their first three calf crops were used to determine effects of single-trait selection for blood serum insulin-like growth factor 1 (IGF-1). Twin heifers were offspring of Simmental sires and Hereford × Simmental or Hereford × Angus dams. All 16 heifers were mated with the same Simmental bull in each year of the study to produce calves born in 1989, 1990 and 1991 (no. = 16, 13 and 10, respectively). Although differences were noted in performance of progeny from the four twins with the highestv.the four with the lowest IGF-1 concentrations, they zoere not large enough to recommend single-trait selection for blood serum IGF-1 in beef heifers.

Preliminary results on between and within twin set variation in insulin-like growth factor I (IGF-1) and some relationships with performance traits in identical twin heifers

Blood samples were collected from eight sets of Simmental crossbred identical twin heifers at 291. 328, 254, 656 and 684 days of age and were assayed for serum concentrations of insulin-like growth factor 1 (IGF-1). The between twin set intraclass correlation for IGF-1 at these ages was −0.08±0.38, 0.25±0.35, 0.62±0.23, 0.68±0.21 and 0.54±0.27, respectively. Residual correlations of serum IGF-1 concentrations with weights taken at the same ages ranged from 0.29 (P > 0.10) to 0.74 (P < 0.01). Heifers with higher serum IGF-1 concentrations at 291, 354, 656 and 684 days of age tended to be taller at 291 and 656 days of age with correlations ranging from 0.25 (P > 0.10) to 0.61 (P < 0.05). Correlations of IGF-1 with weight gains were variable in sign and generally nonsignificant. Results indicate that serum concentrations of IGF-1 are positively related to body weight and hip height of beef heifers.

Milk production by grazing cows given different types of diet in late pregnancy

Three experiments were carried out to examine the effects of different types of diet in late pregnancy on subsequent milk production of cows grazing pasture. In experiment one, 17 sets of monozygous twin heifers were fed equal quantities, of metabolizable energy (ME) of either hay or a mixture of hay and grain (1:1). In experiment two, 13 sets of twin heifers were fed equal quantities of ME as either hay or pasture. In experiment three, 22 pairs of mature cows were given equal quantities of ME as either pasture or a mixture of pasture and hay (1:2). In all experiments the amounts fed were estimated to provide for foetal and mammary development and maintain the dam's tissue reserves. No significant differences were obtained in subsequent milk production. The results show that yield and composition of milk of cows fed solely on pasture during lactation was not affected by the type of diet offered in late pregnancy, if fed at levels near maintenance. At this feeding level, hay or mixtures of hay and grain are suitable alternatives to pasture for dairy cows in late pregnancy.

Effects of gastrointestinal nematodiasis on the productivity of monozygous twin cattle. II. Growth performance and milk production.

A study was conducted with homozygous twin heifers, beginning at less than 5 months of age, in which gastrointestinal nematodiasis was maintained very low in one number of each pair by frequent treatment with the anthelmintic, Cambendazole. A moderate natural infection, chiefly Cooperia species and Ostertagia ostertagi, persisted for one year in the non-treated heifers. Treatments were discontinued following parturition. Twenty-three pairs of twins completed lactation periods varying from 39 to 44 weeks. The treated animals produced significantly more milk, milk fat and fat-corrected-milk (FCM) than their controls, the increase in FCM amounting to an average of 191 kg or 6.58%. They also showed an advantage of weight gains of 29.3 kg at 16 months and 23.6 kg immediately prepartum. Compensatory gains occurred postpartum. During the first year of the study both feed intake and feed utilization by the treated animals were significantly improved. The diminished appetite and reduction of the serum albumin and albumin/globulin ratio of the non-treated animals was readily apparent. There were no significant differences between treatment groups in breeding performance or in the birth weight of their calves, with the exception that breeding of five sets of twins had to be delayed 1 to 3 months until the non-treated heifers reached the designated breeding weight. It was concluded that gastrointestinal nematode infection of young cattle can have a relatively long term deleterious effect upon growth performance as well as upon subsequent milk production during the first lactation period.

Growth and reproductive performance of beef females fed high urea-containing diets.

Two thirds of the total nitrogen in a poor quality 50% forage diet was supplied in 1) soybean meal, 2) equal parts of soybean meal and urea, and 3) urea. These diets were fed to 12 sets of monozygotic twin heifers averaging 148 kg and 235 days of age. The twins were used in an imcomplete-block experiment with each pair of twins being considered a block. The diets were assigned to the twin pairs at random and then these diets were randomly assigned within a pair. The heifers were bred when the lighter twin of a pair reached 272 kilograms. Diets had no effect (P > .05) on length of estrous cycle, services per conception, birth weight of calves, milk yield, average daily gain of calves, and interval from calving to first estrus and conception. Gestation length (P < .05) and cow weight at first conception (P < .01) and calving (P < .05) were longer and heavier, respectively, in the females given the soybean meal diet. There were no differences (P > .05) in the ruminal characteristics of steers fed either the urea or soybean diets with either soybean oil or molasses substituted on an equal weight basis. Replacing molasses with soybean oil increased (P < .05) the dry matter and gross energy digestibility of the diets. Fecal nitrogen losses were greater (P < .05) in the soybean meal diet with molasses. Data from this trial indicate that urea can furnish to-thirds of the total nitrogen in diets of beef females without adversely affecting reproduction

The effect of pregnancy in heifers on voluntary intake, total rumen contents, digestibility and rate of passage

In two experiments using twin heifers with one of each pair pregnant, the effect of advanced pregnancy on the voluntary food intake, dry matter digestibility and rate of passage of food residues, was studied. In the first experiment sorghum silage was fed ad lib. In the second experiment lucerne chaff was fed at ad lib. and restricted levels and, in addition to the measurements listed above, the quantity of reticulo-rumen contents was determined in each animal. In both experiments each of the pregnant heifers ate less than their non-pregnant CO-twins, and, on analysis of all the data on ad lib. feeding, the differences were significant (P&lt;0.01). The mean coefficients of dry matter digestibility for the pregnant heifers were significantly (P&lt;0.01) less than those for non-pregnant heifers. This caused a significantly (P&lt;0.01) lower intake of digestible dry matter by the pregnant heifers. Measurements of the contents of the reticulo-rumen and the rate of passage of food particles gave inconclusive results. These experiments demonstrated that there was a depression of voluntary intake in late pregnancy the cause of which is not known. This would be nutritionally significant only when the quality and voluntary intake of food were marginal.

Variation during growth of twin cattle

Phenotypic variances within pairs of monozygotic and dizygotic twin heifers and also genetic variances and heritabilities were calculated for 12 linear body measurements at a sequence of eight ages up to two years old. The 60 pairs of fraternal and 60 pairs of identical twins used were reared as part of a larger uniformity trial in which feeding was effectively ad libitum throughout.Size differences between members of DZ twin pairs were found to be approximately normally distributed with about the same variance for all breeds and crosses. The variance within DZ pairs increased strongly with age, with a marked increase between 9 and 12 months of age and with most body measurements showing a broadly similar trend. On a logarithmic scale DZ variances increased roughly linearly with degree of maturity and at about the same rate in each body measurement. Coefficients of variation within DZ pairs corrected for measuring error had an average value of 2%. They did not change greatly with age, and were roughly the same for most body measurements although width measurements tended to be more variable than average.Coefficients of variation within MZ pairs had a corresponding overall average of 1·4%; they declined rapidly with age from 2·0% to 1·1%, were roughly the same for all body measurements, but at early ages tended to be greater in late than in early maturing body parts. However, they showed no association with the earliness of maturing of a body part provided variation was measured at the same degree of maturity for each body part.Genetic variation increased rapidly with age in all body measurements. The rate of increase with age was greater for late than for early maturing parts. The rate of increase with degree of maturity, however, was about the same for all body measurements. Coefficients of genetic variation increased slowly with age; they had an average value of 1·6%.Estimates of heritability are given at a sequence of eight ages for each of 12 body measurements. They increased strongly with age from 0·14 on average at three months of age to 0·67 on average at two years of age. At any fixed age, early maturing body parts tended to have higher heritabilities than later maturing body parts. However, if heritability was measured at the same degree of maturity in each body part, early and late maturing parts had about equal heritabilities.The present results are compared with those obtained from twin cattle studies in New Zealand, Sweden and Wisconsin, U.S.A.Inferences from twins about genetic variances and heritabilities for unrelated animals are discussed.

Variation in growth and efficiency in twin cattle with live weight and food intake controlled

In an experiment to investigate the interrelationships of genetics and nutrition in the growth of cattle up to 2 years of age, five monozygotic and six dizygotic Ayrshire twin heifers were reared under close nutritional control on an all cubed diet.Two control systems were used. Some animals were fed similar amounts of food, and differences in growth rate and efficiency examined while others were made to grow alike and differences in food consumption and efficiency examined. Overall, similarly fed animals had similar growth rates and efficiencies and similarly grown animals similar food intakes and efficiencies. Variation in growth, food consumption and efficiency was much less than in an ad lib. feeding system.

A preliminary study of the effect of pregnancy and of lactation on the voluntary intake of food by cows.

1. Monozygotic twin cattle were used in a preliminary study of the effect of pregnancy and of lactation on the voluntary intake of food and water, and on eating and ruminating behaviour. Also, results are reported of an experiment with five pairs of monozygotic twin heifers to examine the variation within pairs of twins in voluntary intake of food and water and eating and ruminating behaviour.2. Voluntary food and water intakes were measured during the last few weeks of pregnancy and during early lactation. Within each twin pair one twin was pregnant or lactating and the other non-lactating and not pregnant, and the food and water intakes of a pair of twins were measured simultaneously.3. On average the variation in voluntary intake of hay within pairs of non-pregnant, monozygotic twin heifers was 0.2 kg or 3 % of the mean daily hay intake.4. The effect of pregnancy was observed in six pairs of twins and in five of the pairs the pregnant animal ate iess hay than its non-pregnant twinmate; in four of these five pairs the effect was small (13 % ). Changes in eating and ruminating behaviour associated with pregnancy were small; the pregnant animals ate concentrates and hay more slowly and ruminated longer than the non-pregnant animals.5. Lactation was associated with a mean increase of 29 % in hay intake in eight out of the nine pairs studied. In four pairs of twins given a diet of concentrates alone the lactating animal ate on average 8 % more than the non-lactating animal. The lactating cows tended to eat concentrates and hay more quickly than the non-lactating cows; because of differences in the ratio of hay to concentrates it was not possible to interpret the changes in rumination that occurred with lactation.

Body size and conformation in identical twin cattle

SUMMARYThe variation and covariation of 12 linear body measurements within 60 pairs of monozygotic twin heifers is analysed in terms of a twin's mean size over a two-year period.Possibly all the covariation, and two thirds, on average, of the variation can be accounted for by a single factor common to all the measurements.Interpretation of this factor shows that a twin is a more or less proportional replicate of its identical co-twin. This proportionality, however, is somewhat distorted because of relatively greater differences in the later maturing body parts.Finally it is shown that the predominant differences in both size and shape can simultaneously be described as twin lagging behind identical co-twin by 0±11·8 days' growth.

Milk Production and Growth of Identical Twin Heifers Calving for the First Time at Two and Three Years of Age

Summary Five identical-twin heifers, calving for the first time at 3 yr., were more persistent in lactation than their mates, which started their second lactation at 3 yr. The early-calving heifers reached a higher peak production than did the late-calving heifers, but ended the lactation with slightly less total milk, on the average. Four- and five-year lactations did not appear to be affected by the age of first calving. Growth or body size was not affected by the different ages of freshening after both groups had completed one or more lactations.

Conformation of twin and quadruplet freemartins

1. Observations were made at 2 years of age on 25 freemartins and their castrated brothers. Three of the freemartins belonged to a set of 4-egg quadruplets. For comparison there were 93 normal pregnant twin and single-born heifers and 14 males twin to males.2. Twelve body measurements on each animal were taken. Averages for each character for 25 single-born Ayrshire heifers and for 10 single-born Friesian heifers were used as standards for comparison with the various groups of twins of like and unlike sex, triplets, and quadruplets.3. Normal twin heifers were slightly smaller in all respects than the standard. Freemartins were also smaller but more so. The quadruplet freemartins were smaller still, but at 2 years they had the live-weight of normal heifers only 1½ years old. Twin males, whether from like or unlike-sexed pairs, were on average slightly smaller than the standard.4. Percentage deviations of each group mean from standard varied systematically when characters were listed in a pre-determined order based on earliness of maturing. This relation has been summarised for each group by the regression of the percentage deviation on order of maturity, the order beginning with head width, and ending with the widths of hooks, pins, and chest. Each available group differed significantly from the chosen standard in conformation in such a way that the later a character appeared in the order, the less it exceeded, or the more it fell short of the standard.5. As judged by the size of these regression coefficients, males twin to males showed the greatest difference in conformation from normal single-born females. Males twin to freemartins showed a slightly smaller difference. Freemartins were intermediate but closer to males. Fertile twin females and single-born females differed very little. These relations held at both 2 years of age and a live-weight of 650 lb. (1½ to 1½ years).6. The quadruplet freemartins were anomalous in having the linear dimensions of immature normal instead of freemartin females of the same weight as if their early maturing body characters had been permanently retarded during slow growth before and after birth.

Relationship of Vit. A and Carotene to Bovine Serum Proteins.,

SummaryBovine serum protein was fractionated with a continuous flow electrophoresis apparatus. Vit. A and carotene were principally associated with albumin. When one co-twin of identical twin heifers was subjected to Vit. A deficiency, serum albumin was progressively reduced. Following an intravenous injection of carotene, the deficient heifer low in serum albumin retained approximately one-half the plasma-carotene concentration as her normal co-twin. Serum albumin returned to normal in the deficient co-twin within 10 days following intravenous Vit. A administration.

The Effect of Nursing Calves on Milk Production of Identical Twin Heifers

Summary Four pairs of identical twin heifers of the Jersey and Guernsey breeds were used in six lactation periods to compare the production of heifers milked in the usual manner with that of heifers that nursed their calves until they were of vealing size. Milk production in the first week after vealing averaged 5.1 lb. per cow per day lower in the nursed group than in the milked group. Lactation of the nursed groups increased gradually after vealing until at 6 weeks the groups were producing equally. The total loss of milk due to the calf nursing averaged 1,496 lb. per cow.

The effect of unequal intervals between milkings upon milk production and diurnal variation in milk secretion.

Five pairs of twin heifers were milked twice daily at intervals of either 11 and 13 hr or 8 and 16 hr for a period of 16 weeks. Total milk and fat production were recorded and, from determinations of residual milk, secretion rates during each interval were estimated. Total milk production was slightly, not significantly, higher in the group subjected to unequal intervals. It was estimated that any depression of production due to intervals even as widely disparate as these is likely to be very small. Fat percentage was unaffected by treatment. Evidence of diurnal variation in milk or fat secretion under the influence of a schedule of 8 and 16-hr intervals was not conclusive, but overall there was no significant evidence that secretion rates were lower during the longer interval.

The effect of undernutrition before calving on the quantity and composition of milk produced by two-year-old heifers

Six pairs of 2-year-old monozygous twin heifers were used to determine the effect of underfeeding for 10 weeks prior to calving. Those which had been well fed before calving produced more milk than their sisters which had been poorly fed.There was no effect on milk or butterfat composition, probably because none of the animals lost much weight after calving.The effect of the treatment differed markedly between twin pairs, the maximum difference in milk yield being 2866 lb., the minimum 135 lb., and the mean 1057 lb. for 270 days' lactation.The ratios of between-twin-pair to within-twin-pair variance for butterfat, total protein and lactose percentages of the milk were as follows: