Comparison of Three Mating Systems: II. Weights and Body Measurements of Heifers1

C o m p a r i s o n o f T h r e e M a t i n g Systems: II. Weights and B o d y M e a s u r e m e n t s o f Heifers 1 R. H. MILLER, R. E. PEARSON, L. A. FULTON, R. D. PLOWMAN 2, N. W. HOOVEN, JR., M. E. CREEGAN, and J. W. SMITH USDA, ARS, Animal Physiologyand Genetics Institute Beltsville, MD 20705 ABST RACT

Body dimensions and weights of female progeny from three systems of mating were studied from birth to first calving. Heifers produced by outcrossing to Holstein sires in artificial insemination were largest up to first calving, at which time the average of heifers produced by crossbreeding (Ayrshire, Brown Swiss, and Holstein sires) exceeded the outcrosses in weight and body length from withers to pins. Heifers produced by mild inbreeding within a separate line were consistently smaller than outcrosses and crossbreds. Brown Swiss × Holstein heifers were largest of the six crosses; Ayrshire × Holstein crosses were smallest. Brown Swiss × Holstein crosses were also larger than both purebred Holstein groups. Heifers born in November and born of fourth parity dams were generally larger than heifers born in other seasons or of other parity dams, either in weight or in aspects of b o d y dimension. INI~RODUCTION

Only two methods for genetic change are available to the breeder: Selection or some form of crossing. This report concerns the growth of heifers through first calving under different types o f mating systems. Mating systems leading to inbreeding have reduced birth weights by .11 kg and weights at 48 mo by 2.3 kg for each .01 increase in inbreeding coefficient (27, 28). Swett et al. (21) observed a 15% decline in body weight of 49 Holsteins inbred from 10 to 69%; however, skeletal size of these animals was not affected

Received May 2, 1977. 1Part of Regional Project NC-2, Improvement of Dairy Cattle through Breeding. 2Western Region, ARS, Utah State University, Logan 84322. 1977 J Dairy Sci 60:1787--1798

by inbreeding. For some workers inbreeding had no effect on mature size (1, 28) whereas others (4) have shown that effects of inbreeding on size decreased with age. Mildly inbred cattle (13% inbred) studied by Brum et al. (3) were 3% lighter in weight and less than 1% smaller in some other measurements than were linecrosses at 12 and 19 too; results o f M i et al. (16) were similar. Voelker and Tucker (26) found linebreds and linecrosses intermediate in size at all ages to outcrosses and inbreds. Holtmann et al. (11) found significant differences between inbred and outbred Holsteins for body measurements from birth through 90 days postpartum. Outbreds were larger in all measurements at each age, but the differences became smaller with age. Hollon et al. (9, 10) crossed Brown Swiss, Holstein, Jersey, and Red-Sindhi and found purebred Holsteins larger than crossbreds in b o d y weight at all ages by 3 to 17%. Crosses by purebred sires were larger than those by crossbred sires. The magnitude of the differences was greater after 12 mo of age. Workers generally agree that crossbreds exceed the mean size of their parents (8, 14, 15, 20, 24). Touchberry (22) classified six b o d y measurements into those involving the skeletal and fleshing growth. Shreffler (20) found that differences in fleshiness between purebreds and crossbreds were significant at 18 and 24 mo but skeletal differences were not significant at any age. Batra and Touchberry (2) for Guernseys, Holsteins, and their crosses concluded that nonadditive genetic effects are relatively small for measures of size compared to additive genetic differences between and within these two breeds. Several workers (14, 15, 24) have found that heterotic effects decrease linearly with increasing age. Percentage increases were greater for weight than for b o d y measures and were also greater for measures of fleshiness than for measures of skeletal growth. McDowell et al. (14) found Jersey × Red Sindhi F1 crossbreds were taller and had greater width and depth at

1787

1788

MILLER ET AL.

earlier ages than purebred Jerseys; however, body length of crossbreds was less. Coefficmnts of variation for weight and dimensions were the same for both groups. McDowell et al. (15) found that gains of two-breed crosses among Ayrshire, Brown Swiss, and Holstein were faster with advancing age than were the mean gains of their parents. At 16 too, the average advantage of crossbreds was about 12 kg/female. In this study, crossbreds usually did not exceed purebred Holsteins in body weight. Touchberry and Bereskin (24) found that crossing Guernseys and Holsteins increased growth rates up to 2 yr. Beyond this age, purebreds grew at a faster rate. Crossbreeding effects appeared to be expressed more in rate of development than in ultimate mature size. For size and rate of growth, apparently more was to be gained from additive genetic variation between and within the two breeds than from nonadditive variation. Touchberry et al. (20, 23, 24) found significant effects of breed of dam at all ages for every measurement were consistently larger than the effect of breed of sire that did not become significant until animals were 12 mo or older. After 24 mo, these differences were not statistically significant. Calves of Holstein dams were 20% heavier at birth than those of Guernsey dams, and calves of Holstein sires were 9% heavier at birth than those of Guernsey sires. Differences between these breed groups were significant for all ages and all measurements. Second- and third-generation crossbreds were intermediate to purebreds but nearer Holsteins at early ages. Donald et al. (6) with two- and three-way crosses among Ayrshire, Holstein, and Jersey found that smaller dams had lighter than expected crossbred progeny whereas larger dams had heavier than expected offspring. The wider the cross in terms o f parental size, the greater were the deviations from mid-parent weights. Thus, mean birth weight, while showing midparent inheritance, was subject to maternal control that appeared to be proportional to the b o d y weight of the dam and her own birth weight. The mean birth weight of three-breed cross calves also was modified in the direction of the dam's own mean birth weight. No carryover effects from differences in birth weights of the reciprocal two-breed crosses could be detected in three-breed cross calves. Dickinson (5) showed that crossbred progeny of dams of Journal of Dairy Science Vol. 60, No. 11, 1977

small breeds gained more rapidly than the reciprocal cross from dams of large breeds. With monozygotic and dizygotic twins, Gibson and Watson (7) found that the ratios of within-pair variance in daily gain indicated that differences in performance were most dependents on genetic differences at 12 to 24 and at 52 to 72 wk of age.

METHODS

The data were from females produced in a project on mating systems at Beltsville between 1957 and 1969. Outcross (OC), mildly inbred (MI), and crossbred (CB) animals were produced from a common Holstein-Friesian (H) foundation herd. The design o f this project and the assignment of foundation females to groups was described b y Pearson et al. (18). Outcross sires were selected from among those in AI that had no ancestors in common with the foundation herd for at least three generations. Mildly inbred sires were chosen from those produced at Beltsville and progeny tested at other locations. Two- and three-breed crosses were formed by sires chosen from Ayrshire (A) and Brown Swiss (S) sires available in artificial insemination (AI); backcrosses were formed by using OC Holstein sires on the three-way crosses. Selection of the 42 sires was based primarily on their ability to increase milk production. Matings were to provide 15 to 20 daughters from each sire; however, the number of live daughters each sire produced differed widely. There were 236 OC, 220 MI, and 199 CB females born. Crossbred animals included 34 A x H , 32 S×H, 40 S x A x H , 34 A × S × H , 35 H× Sx A× H, and 24 H× A× S× H (breed of sire is listed first). All females from these mat!n_gs were assigned to the project; however, 168 animals failed to reach first calving for observation because of reproductive failure, death, or other involuntary reasons. Calf mortality by 6 mo of age was 11.0, 5.9, and 10.1% for OC, MI, and CB. The total mortality rate of 66 first-generation crosses was 4.6%; and the rates in second and third generations were 12.2 and 13.6. Calves were separated from dams at 24 h and moved to individual solid-wall stalls. Calves were moved to community pens with exercise lots at 30 days and were confined individually there during feeding. On birth weight calves were fed 2.7 to 3.6 kg of milk daily, half at

WEIGHTS AND MEASUREMENTS OF HEIFERS each feeding. This volume was adjusted at 10day intervals by increasing .45 kg for each 4.5 kg of body weight to a maximum of 6.4 kg. Milk was fed until 180 days. Hay, water, and a concentrate ration of 11.6% crude protein were offered to the calves at 2 wk. By 30 days, concentrate was fed at .45 kg/day, and this amount was increased to 1.8 kg daily by 180 days. From 6 mo to 12 mo, 1.8 kg grain continued to be the maximum concentrate allowance; hay was continued free choice. All animals were under as uniform a plan of feeding as possible; however, during the study, minor changes were made. From 12 to 16 mo, the heifers were fed individually 1.4 kg of concentrate daily and U.S. No. 1 alfalfa, light grass mix hay ad libitum. At 16 mo, heifers were moved to open-shed housing where they had access to either pasture or dry lot feeding according to the season. During this period, hay and corn silage were fed along with enough concentrate to maintain growth at about .68 kg daily. Heifers were grouped separately after being diagnosed pregnant and allowed up to 2.3 kg of concentrate daily. The heifers were moved into maternity housing 10 to 14 days prior to due date where they were fed a ration for milking. Feeding and management of lactating animals were described previously (12, 17). Breeding commenced at age 15 mo. If an animal was not pregnant by 24 too, breeding was ended. The average age at conception was 16 too. Body weights in conjunction with linear measurements were obtained within 3 days of the date of measurement. Linear measurements for height of withers (W), length from withers to pins (LWP), and from withers to hips (LWH), depth and circumference of chest (DFC, CFC) and of paunch (DP, CP) were obtained within 15 days of the ages of 6, 12, and 16 mo, and at 90 days postpartum. Linear measurements were with metal calipers that included a leveling vial in the horizontal arm. Circumferential measurements were with a metallic woven tape. Both readings were taken to the nearest .5 cm. In accord with Touchberry and Lush (25), only single observations were obtained. Animals were positioned on a level floor with legs perpendicular. The head was held straight forward and level with the back. An imaginary perpendicular line extending through the mid-point of the foreleg es-

1789

tablished the point of withers which was then marked with chalk. This reference point then was used for both the measurement of W and the point from which LWH and LWP were measured. In these measurements, the long arm of the caliper rested along the median line of the animal; and base was at the point of withers, and the cross arm flush against the pinbone. Length to hips was determined at the time of pinbone measurement by noting the length at a transve/'se line between the highest point of the two hips. Depth of chest was measured with one horizontal arm resting on the chest floor just behind the forelegs and, with the caliper perpendicular, the second arm leveled on the vertebra. The DP was measured at the 13th or last rib. Circumferences of chest and CP were taken at the same locations with the tape drawn tightly around the body. The data combined over all ages were analyzed by the following least-squares mixed model: Yijk~mno =/.t + m i + bj + sk + (g/s)k~ + Pm + (bS)jk + ck~ n + ao + (sa)k o + eijk~mno where m i represents an effect of the ith month of birth (i = 1, 2 .... 12); bj is a contribution due to the jth year of birth (j = 1958, 1959, ..., 1969); sk is an element for the k th system of mating (k = 1, 2, 3); (g/s)k~ is an effect of the ~th generation or type of cross within the k th system of mating; Pm is'a contribution due to the m th parity of birth (m = 1, 2, ..., 6); (bs)jk represents the interaction of year/" with mating system k ; Ckl n is the residual random effect of the nth animal in the J2th generation of the k th mating system; ao represents the effect of the oth age (o = 1, 2, 3, 4 for body measurements and o = 1, 2, ..., 5 for body weight); (sa)ko is the interaction of the oth age with the kth system of mating; and eijk•mn o is a residual within-animal error term. All elements were fixed except for Ck£n and eijk~mno. Parities of birth were 1 to 5, and 6 or later. Weight also was analyzed separately to include birth weights. Limitations on matrix size prohibited fitting models with interactions of age with parity or month of birth. Also, interaction of age with generation only could be examined separately by omitting the interaction of year x mating system. When this was done, age x generation was significant in some instances but did not affect materially conclusions about mating sysJournal of Dairy Science Vol. 60, No. 11, 1977

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T A B L E 1. Results o f tests o f s i g n i f i c a n c e f o r b o d y m e a s u r e m e n t s a .

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Source

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Month Year Mating system Generations/OC c Generations/MI c Generations/CB c Parity of birth Year X mating systems Residual animals Ages Ages X m a t i n g s y s t e m s Error

a, b

= P<.05;**

11 11 2 3 3 5 5 22 528 3 6 1,615

Depth

Circumference

Wither height

Chest

Paunch

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= P<.01.

•

W e i g h t analysis i n c l u d e d b i r t h w e i g h t .

C o c = O u t c r o s s , MI = Mild i n b r e e d i n g , CB = C r o s s b r e d .

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TABLE 2. Least-squares means of mating systems by age a. Length Age and mating system a

Obser.

Wither height

Circumference

Depth Chest

Paunch

Chest

Paunch

Withers to hips

127.7 125.2 125.7

161.4 153.3 157.3

64.6 63.3 63.7

Withers to pins

(cm) 6-month OC MI CB

206 201 179

105.7 103.9 104.5

48.2 47.3 47.6

53.1 51.0 51.8

96.3 94.1 95.6

X >

m

g < o o~ o

12-month OC MI CB

198 193 171

120.2 118.9 119.1

58.8 58.2 58.6

61.8 59.8 60.8

157.7 155.2 156.2

189.5 179.5 185.0

78.2 76.7 77.7

116.8 115.0 116.7

16-month OC MI CB

204 195 177

126.0 124.6 124.8

63.3 62.5 62.6

65.8 63,3 64.8

170.6 168.2 169.1

205.0 195.7 201.5

83.5 81.7 82.2

125.3 122.8 124.8

1st lactation OC MI CB

174 170 143

134.7 133.0 133.4

70.5 69.6 69.7

73.3 71.2 71.8

187.1 185.0 186.0

227.8 219.8 223.6

91.9 90.1 90.4

138.3 135.3 138.4

z o

a o c = Outcross, MI = Mild inbreeding, CB = Crossbred.

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1792

MILLER ET AL.

terns, generations within MI, "generations" of CB, parity, or month. Strictly speaking, tests of significance based on analyses of weights and measurements combined for all ages may be inaccurate because of a correlation of mean and variance. An analysis of log (body weight) was compared with untransformed results. Significance tests led to the same conclusions, except for parity of birth, which was significant for logs but not for untransformed weights. On these results, we decided to use the analyses of untransformed data. RESULTS A N D DISCUSSION

Analyses of variance tests of significance are in Table 1. Mating systems differed for all traits (P<.01). Generations within OC were significantly different only for LWH (P<.05). Generations vdthin MI differed for weight, W, CFC, LWP (P<.05), and CP (P<.01). Crossbred groups were different for weight, W, LWH, and LWP (P<.01), and for CFC (P<.05). Months of birth were different only for body weight (P<.05) and CFC (P<.01). Years of birth differed for all traits (P<.01). Parities of birth differed for DFC, and DP (P<.01) and for CFC (P<.05). Interaction of years with mating systems was significant for all traits, either at .05 or .01. Interaction of age by mating system was significant only for weight and LWP (P<.01). Least-squares means for the body measurements by groups of age x mating system are in Table 2, and the corresponding results for weights are in Table 3. The significant interaction of age x mating system for weight and LWP was due to faster rate of growth of crossbreds. Crosses were on the average lighter and shorter than outcrosses at birth and 6 too, but by 90 days after first calving they were heavier than outcrosses (562 kg vs. 558 kg). Mild inbreds were consistently lighter and smaller than both outcross and crossbreds from birth to first calving. The differences were especially large at b i r t h - m i l d inbreds weighing 34 kg, compared to 42 kg for outcrosses. At 90 days post-first calving, mild inbreds were 20 kg lighter, 3 cm shorter in LWH, 2 cm less in CFC and .9 cm less DFC than outcrosses. At 90 days after first calving, crossbreds were 1.3 cm less than outcrosses in W, .8 cm less in DFC, 1.1 cm less in CFC, and 1.5 cm less in LWH, than outcross Journal of Dairy Science Vol. 60, No. 11, 19"77

TABLE 3. Least-squares means of body weight for age - mating system groupsa. Age and mating system a

No. observ.

Weight (kg)

Birth OC MI CB

204 195 177

41.5 34.2 37.4

6-month OC MI CB

206 201 179

201.8 186.6 195.3

12-month OC MI CB

198 193 171

341.6 322.9 333.2

16-month OC MI CB

204 195 177

423.4 402.4 417.1

1st lactation OC MI CB

174 170 143

558.1 537.6 561.6

aoc = Outcross, MI = Mild inbreeding, CB = Crossbred.

but crossbreds were equal to outcrosses in weight and LWP at this stage. Foundation cows producing OC and MI progeny weighed 191 kg and 190 kg at 6 mo of age. Table 3 shows that OC progeny were heavier and MI progeny were lighter than foundation animals at this age. The differential rate of weight increase of CB is in Fig. 1. Differences were similar, though smaller, for most of the body measurements; however, CB were smaller than OC at first calving in all linear measurements except LWP. Crossbreds tended to be closer to OC in paunch dimensions. Thus, the faster growth rate may have been caused by a greater degree of fleshiness of crosses than of outcross Holsteins. The data in Table 3 may be compared with Holstein growth standards by Ragsdale (19) and Matthews and Fohrman (13). This shows that OC and MI animals exceeded both the Ragsdale and Matthews standards, except that MI were lighter at birth. Outcross heifers exceeded the Ragsdale standards by 3, 25, 19, 19, and 7% at

WEIGHTS AND MEASUREMENTS OF HEIFERS

179

600

500 .-- j l

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"-: 400

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300

200

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"

----Mild Inbreeding

100

Birth

I 6 Months

I

i

12 Months 16 Months

i

1st Lactation

AGE

FIG. 1. Weights of outcross, mild inbred and crossbred heifers from birth to first calving.

birth, 6 mo, 12 mo, 16 mo and after first calving. Matthews' and Fohrman's standards were intermediate. Thus, over time there apparently has been either a biological change in the Holstein breed, a change in heifer management regimes, or a combination of both, such that present-day Holstein heifers are larger than accepted past standards for a given age. Least-squares means for generations of MI are in Table 4. There were no significant differences among generations of OC, except for LWH; hence, these means are not presented. Means for weight exclude birth weight to make them comparable with the means of linear measurements. Differences among generations of MI were nonsignificant for DFC, DP, and LWH. Generation 1 weight was significantly heavier than that of later generations (P<.05). Similarly, first generation MI exceeded all other generations for dimensions of W, CFC, CP, and LWP. Consistent downward trends were observed for weight, W, CFC and CP. generations 2 and 3 were about equal, and generation 4 was lowest. To determine whether inbreeding might account for this depression in b o d y weight, mean inbreeding coefficients were computed. These were 2.6, 2.9, 3.2, and 3.1% for first, second, third, and fourth generations. According to Young et al. (28), depressions of 1, 3, 4, 5, and 9 kg can be expected at birth, 6, 12, 18, and 24 mo with an increase in inbreeding of 3%. Thus,

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Journal of Dairy Science Vol. 60, No. 11, 1977

1794

MILLER ET AL.

some factor other than inbreeding must account for the decreased size of MI. An obvious explanation would be sire differences. As reported by Pearson et al. (18), sire and generation are confounded partly in these data. Least-squares means for types of crossbreds are in Table 5. Differences were significant except for DFC, DP, and CP. Crosses S× H were heavier, taller at withers, greater in circumference of chest, and longer from withers to pins and withers to hips than other crosses. Likewise, A× H crosses were lightest in weight and smallest of all crosses in CFC and LWH. The mean weight of Sx H crosses at first calving was 607 kg, compared to 535 kg for AXH and 558 kg for the average of OC Holsteins. The two three-way crosses and the two backcrosses were generally intermediate in size. Because of the absence of purebred S and A females in the design, it is not possible to assess heterosis in the size and growth of crossbreds. However, the fact that the average of all crosses had a faster weight gain than the average of all outcross H suggests some heterosis and that this may have been most evident in the Sx H cross. Relating these results to production performance, Pearson et al. (18) found that the H×S (AH) backcross had the highest milk yield in this experiment. Thus, the SxH cross appears to have merit for size and growth but not for milk yield. Least-squares means for month of birth are in Table 6 for the traits exhibiting differences (weight and CFC). Weights in Table 6 are from the analysis excluding birth weight, to be comparable to the means for CFC. The peak for weight and CFC occurred for animals born in November. Animals born in December to April had lowest weights and CFC. Births in May to October were more intermediate in weight and CFC. Most workers (24) have found no differences in calf growth or birth weight as a result of season of birth. The trends in Table 6 are averaged over ages and are expressed on a scale corresponding to around 15 mo of age. Thus, these effects may be due to either differences in size at birth or differential rate of growth thereafter, or a combination of both reasons. Analysis of birth weight alone indicated that month of birth had no effect. Hence, under the environmental conditions in this herd, calves born in December to April grow more slowly than Journal of Dairy Science Vol. 60, No. 11, 1977

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WEIGHTS AND MEASUREMENTS OF HEIFERS

1795

TABLE 6. Least-squares means by month of birth for weight and circumference of chest, a

Weight

Circumference of chest

(kg)

(cm)

369.5 367.6 366.7 366.0 371.0 375.5 374.5 377.4 378.3 379.6 382.2 367.1

158.9 159.3 157.9 158.8 158.4 159.9 159.5 160.0 160.3 160.7 161.3 158.6

No.

Month

observ.

January February March April May June July August September October November December

224 157 119 143 142 211 192 178 144 208 252 245

Significance levelb aAveraged across ages. b** = P<.01.

those born at o t h e r times during t h e year. Calves b o r n f r o m D e c e m b e r t h r o u g h April may suffer f r o m a high f r e q u e n c y o f calfhood diseases, perhaps caused b y exposure to high moisture weather conditions at a critical early period in their growth. A p p a r e n t l y this poor growth is expressed in decreased weight and CFC, rather than lack o f growth in s o m e o t h e r dimension. Feeding regimes probably were not involved because some calves born f r o m December through April w o u l d have g o n e on pas-

ture at 6 mo, and others w o u l d not. Least-squares means for parity of dam are in Table 7 for D F C , DP, and CFC (traits for which differences were significant). Differences were small, but there was a progressive increase in these b o d y dimensions f r o m first-parity to fourth-parity births. D e p t h of chest changed little in fifth- and sixth-parity births, while DP decreased in fifth- and sixth-parity births and CFC decreased in fifth-parity and increased slightly in sixth-parity births.

TABLE 7. Least-squares means for parity of dama. Depth

No.

Parity

observ.

Chest

Paunch

Circumference of chest

(cm) 1 2 3 4 5 6

809 621 465 172 62 86

Significance levelb

59.2 59.6 60.0 60.0 59.8 59.8

61.3 62.3 62.8 63.0 62.6 62.2

158.6 159.6 159.6 160.8 158.8 159.4

**

**

*

aAveraged across ages. b, = P<.05;** = P<.01. Journal of Dairy Science Vol. 60, No. 11, 1977

1796

MILLER

These trends agree with previous reports for body weight which have indicated that animals born to first-parity dams are slightly smaller than average. In an environment o f dairy cattle, such differences must be due almost exclusively to prenatal effects, to any differences in antibody competence of colostrum, and to any effects on the calf of degree of ease or difficulty in calving. Altogether, the differences of body dimensions due to parity of birth are small and not different for average b o d y weight. The practice in this herd was to breed heifers after 15 mo of age. Mean weight 90 days after first calving ranged from 538 kg for MI to 562 kg for CB. Thus, parity of birth effects may not have been large due to the adequate s~ze attained by heifers at their first breeding and first calving. Estimates of year means (Table 8) showed no consistent trends. Weight, DFC, DP, CFC, CP, and DP appeared to peak in the 2nd yr (1959) whereas W, LWH, and LWP peaked in 1966. However, values in other years were near the highest values, suggesting randomness in the year-to-year differences. The year means suggest that genetic effects (mating systems and generations) and environmental effects were separated with some success in the analysis. Environmental effects generally would be expected to behave randomly over time when efforts to maintain a consistent environment have been successful. Confounding of year and generation would be expected to lead to negative correlations between the estimates of these effects. However, comparisons of the year trends with the means for generations o f MI and types o f crossbred do not indicate the presence of such correlations. For example, MI were highest in generation 1, and S× H crosses were highest of CB types, while most measurements were highest in 1 9 5 8 - 5 9 (generation 1 and S× H crosses were produced primarily in the early years of the experiment).

ET AL.

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SUMMARY AND CONCLUSIONS

Body dimensions and weights of female progeny from three systems of mating (OC, MI, and CB) were studied from birth to first calving. Outcross females were largest up to first calving, at which time the average of all CB exceeded OC in weight and LWP. Mild inbreds (average inbreeding 3%) were consistently smalJ o u r n a l o f D a i r y S c i e n c e V o l . 6 0 , N o . 11, 1 9 7 7

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WEIGHTS AND MEASUREMENTS OF HEIFERS let t h a n b o t h OC and CB. This d e p r e s s e d b o d y size was p r o b a b l y n o t solely a t t r i b u t a b l e t o eff e c t s o f inbreeding. Both p u r e b r e d H o l s t e i n groups (OC,/Vii) exc e e d e d t h e g r o w t h s t a n d a r d s o f Ragsdale a n d M a t t h e w s , indicating a change in m a n a g e m e n t regimes for heifers or a biological change in t h e H o l s t e i n breed, or b o t h . B r o w n Swiss × H o l s t e i n crosses were largest o f t h e six crosses p r o d u c e d , and A× H crosses w e r e smallest. B r o w n Swiss × Holstein crosses also e x c e e d e d b o t h p u r e b r e d H o l s t e i n groups. A n i m a l s b o r n in N o v e m b e r were heavier in weight and larger in f o r e c h e s t c i r c u m f e r e n c e , t h a n animals b o r n during o t h e r m o n t h s o f t h e year. Increasing parity o f b i r t h favored larger size f r o m first parity up to f o u r t h parity, w i t h res p e c t t o D F C , CFC, and DP. Mating s y s t e m s p r o d u c i n g i n b r e e d i n g result in r e d u c e d b o d y size and g r o w t h . Crosses o f B r o w n Swiss bulls o n H o l s t e i n cows m a y prod u c e females t h a t are larger t h a n p u r e b r e d Holsteins. B o d y size o f heifers is i n f l u e n c e d b y b o t h season and parity o f b i r t h .

REFERENCES

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