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Arkansas Animal Science Department Report 2001 mer of 1999, droughty growing conditions limited the availability of forage; therefore cattle were supplemented for ad libitum intake with bermudagrass hay and sudangrass baleage. In mid-June, 1999, when the heifers averaged approximately 12 mo of age, two blood samples were obtained 10 d apart for each heifer for progesterone assay. Heifers were considered cycling at 12 mo of age when concentration of progesterone in one of the two samples was ≥ 1 ng/ml. In late August, heifers were split into two groups based on chronological age, and heifers in the oldest of the two groups were then synchronized and bred AI on observed standing heat. Estrus detection was accomplished by 24 h monitoring with the Heatwatch System. The second group of younger heifers were synchronized 3 wk later and bred as stated above. Artificial insemination was halted on November 15, 1999. Heifers were checked after 60 d of gestation for pregnancy using ultrasonography. Data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). Sources of variation in the dependent variables of weight, hip height, chest depth, and body condition score were partitioned using a mathematical model that included terms for an overall mean, breed type, age, breed type x age interaction, and residual error. Least squares means were separated using repeated t-tests in the LSmeans option of PROC GLM of SAS. The distributions of heifers cycling and pregnancy rate were tested using Chisquare statistics. Results and Discussion Body Weight. The interaction of breed type x age was not significant for BW at 6 mo, but it was an important source of variation in BW at 14 mo for replacement dairy heifers in this study. This may indicate that compensatory growth occurred from 6 to 14 mo of age. These results are in agreement with those of Ruvuna et al. (1986) who reported that crosses of Holstein, Jersey, and Brown Swiss were superior to purebreds for growth. At 6 mo of age the BSH heifers were heavier (P < 0.05) than both H and JH heifers, but by 14 mo of age mean BW for the H and BSH heifers were similar (P > 0.05, Figure 1). At 6 mo of age the H heifers in our study had smaller mean BW than the industry standards reported by Henrichs and Losinger (1998). However, by 14 mo of age the H heifers in our study were approaching the industry standard range for mean BW, probably due to compensatory growth from 6 to 14 mo of age. It appears that the forage-based system for heifer development was adequate for growth. Henrichs and Losinger (1998) reported that H heifers developed in the Southeast U.S. had lower BW when compared to H heifers developed in other regions. Differences in photoperiod, feeding strategies, and/or predominant forage types in various regions of the U.S. could explain the differences in growth (body weight:age) between the regions. Hip Height. Skeletal size or frame development is often emphasized as a key factor in replacement heifer rearing programs. Traits that reflect long-bone growth may reflect true size of replacement heifers better than BW because BW is influenced by pregnancy and body condition. In our study the interaction of breed type x age was significant for hip height at 6 mo of age, but not at 14 mo of age (P > 0.05). The BSH heifers were taller (P < 0.05) than the two other breed types at 6 mo of age, but by 14 mo of age H and BSH heifers were similar (P > 0.05) for mean hip height (Figure 2), and were similar to the industry standards for range in mean wither height (Heinrichs and Losinger, 1998). Because hip height reaches maturity before wither weight in beef cattle (Brown et al., 1983), it is expected that heifers in our study would be taller at the hip than the industry standard for wither height at 6 mo of age. However the heifers in our study were shorter in hip height than the industry standards for wither height (Heinrichs and Losinger, 1998), indicating that our heifers had not achieved sufficient long bone growth to 6 mo of age. Mean hip heights for H, JH, and BSH heifers were 40, 38, and 39 inches, respectively, compared to an industry standard range of 40 to 42 inches for H heifers measured at the withers at 6 mo of age. Depth of Chest. The interaction of breed type x age and the main effect for breed type were not significant for depth of chest at 6 or 14 mo of age. The three breed types ranked highest to lowest for mean chest depth at 6 mo of age were BSH, JH and H and at 14 mo of age were H, BSH, JH (Figure 3). Age was a significant (P < 0.05) source of variation for depth of chest in this study. Body Condition Score. Body condition scores are important predictors of potential reproductive efficiencies of dairy heifers. Mean body condition scores of the three breed types of heifers were similar (P > 0.05, Figure 4). Mean body condition score of heifers in our study exceeded (3.0 to 3.1 vs. 2.2 to 2.8) those of H heifers reported by Hoffman (1997). Reproductive Performance. Reproductive performance of heifers is important because of the proportion of heifers culled for reproductive failure and because reproductive efficiency determines how soon productive life begins. The reproductive performance of three breed types of replacement dairy heifers is presented in Figure 5. By 12 mo of age, the JH breed group had the highest percentage (90%) of heifers cycling, this was followed by BSH (75%), and then by H (48%, P < 0.05). At about 15 mo of age, the percentage of heifers pregnant was similar among the three breed types. The breed types ranked from highest to lowest in percentage pregnant were: BSH (96%), JH (87%) and H (77%). These data are in agreement with results of previous studies indicating that crossbreeding tends to improve reproductive efficiency in dairy heifers. McDowell (1982) summarized dairy cattle crossbreeding of the S-49 Southern Regional Cooperative Research Project and concluded that crossbreeds tended to surpass purebreds in overall breeding efficiency. Wheat Pasture. Our data shows that wheat pasture may be used for replacement dairy heifer development in Arkansas. However, we acknowledge that these data represent wheat production in one growing season; there are studies with differing opinions about the consistency of production patterns of wheat from season to season. 156
AAES Research Series 488 Implications These results suggest that farmers could potentially raise heifers on forage plus supplements and achieve rapid, economical growth. General considerations on crossbreeding are a change in size and BW early in life and that crossbreeds tend to cycle earlier, breed earlier, and should calve and enter the milking herd younger. Finally, more research is needed to determine alternative development systems for replacement dairy heifers utilizing forage as the primary energy source. Literature Cited Brown, C.J., et al. 1983. Ark. Agr. Exp. Sta. Bulletin. 863. Dickinson, F. N., and R. W. Touchberry. 1961. J. Dairy Sci. 48:879. Ferguson, J.D., et al. 1994. J. Dairy Sci. 77:2695. Heinrichs, A.J., and W.C. Losinger. 1998. J. Anim. Sci. 76:1254. Hoffman, P.C. 1997. J. Anim. Sci. 75: 836. McDowell, R.E. 1982. Southern Coop. Serv. Bull. No. 259. Louisiana State Univ., Baton Rouge, LA. Robinson, O.W., et al. 1980. J. Dairy Sci. 63: 1887. Ruvuna, F., et al. 1986. J. Dairy Sci. 69: 782. Body weight, lb 800 700 600 500 400 300 200 b c a a b a 100 0 6 mo 14 mo H JH BSH Breed -types: H=Holstein, JH=Jersey X Holstein, BSH=Brown Swiss X Holst abc Means within age with different letters differ (P < 0.05) ein Figure 1. Least-squares means for body weight at 6 and 14 mo of age for three breed types of replacement dairy heifers 157
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Arkansas Animal Science Department
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spine copy ARKANSAS ANIMAL SCIENCE
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INTRODUCTION The faculty and staff
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COMMON ABBREVIATIONS Abbreviation T
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The Effects of Nitrogen Fertilizati
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Demographics and Academic Success o
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Efficacy of Mannan Oligosaccharide
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Effects of Dietary Magnesium and Ha
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Effect of Feather Meal on Live Anim
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Maternal Effects for Performance Te
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Supplementation of Beef Cows and He
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Influence of Supplementing Cobalt i
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Long-Term Immune Response of Beef H
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Small Grain Forage for Stocker Catt
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Economics of Production Systems Inv
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