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Title: BOVINE SOMATOTROPIN AND RUMEN UNDEGRADABLE PROTEIN EFFECTS ON SKELETAL GROWTH IN PREPUBERTAL DAIRY HEIFERS

Author
item MOALLEM, U - UNIVERSITY OF MARYLAND
item DAHL, G - UNIVERSITY OF MARYLAND
item DUFFEY, E - UNIVERSITY OF MARYLAND
item Capuco, Anthony
item ERDMAN, R - UNIVERSITY OF MARYLAND

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2004
Publication Date: 10/10/2004
Citation: Moallem, U., Dahl, G.E., Duffey, E.K., Capuco, A.V., Erdman, R.A. 2004. Bovine somatotropin and rumen undegradable protein effects on skeletal growth in prepubertal dairy heifers. Journal of Dairy Science. 87:3381-3888.

Interpretive Summary: The objectives of this study were to determine the effects of dietary rumen-undegradable protein (RUP) and bovine somatotropin (bST) during the period from weaning until puberty on body weight and skeletal growth. From 90 days of age to puberty, bST and RUP increased average daily weight gain in an additive manner. Skeletal growth rates were also increased by both bST and RUP. Growth curves showed that RUP effects on rates of body weight gain and skeletal growth were greatest from 90 to 150 days of age and diminished thereafter, suggesting that protein was limiting during this time period. Conversely, bST effects tended to be greater as heifers approached puberty. Age at puberty was not affected by treatment and averaged 314 days of age. From 314 to 644 days of age, rates of body weight gain and skeletal growth were nearly identical among treatment groups. However, treatment differences present at 314 days of age persisted through 644 days, more than 10 months after treatments ceased. These results suggested that protein during the early postweaning period and bST during the period (200 to 300 days of age) just prior to puberty could be used to accelerate simultaneous increases in both body weight gain skeletal growth rates of dairy heifers without reducing age at puberty.

Technical Abstract: The objectives of this study were to determine the effects of dietary rumen-undegradable protein (RUP) and bovine somatotropin (bST) during the period from weaning until puberty on body weight (BW) and skeletal growth rates. Fifty-one Holstein heifers at 90 d of age were randomly assigned to treatments (n=12 or 13) consisting of 0.1 mg/kg body weight per day of bST and 2% added dietary RUP (dry matter basis) applied in a 2 x 2 factorial design. From 90 to 314 d, bST increased average daily gain (ADG) by 0.07 kg/d and BW by 16.2 kg while added RUP increased ADG by 0.10 kg/d and BW by 21.4 kg. Both bST and RUP effects on BW and ADG were additive. Skeletal growth rates, as measured by withers height (WH) and hip height (HH) were increased by both bST and RUP. Somatotropin and RUP increased WH by 1.8 and 2.7 cm and hip height by 2.5 and 4.0 cm, respectively at 314 d of age. Growth curves showed that RUP effects on rates of BW, WH and HH growth were greatest from 90 to 150 d age and diminished thereafter, suggesting that protein was limiting during this time period. Conversely, bST effects tended to be greater as the heifers approached puberty. Age at puberty was not affected by treatment averaging 314 d across treatments. From 314 to 644 d of age, rates of BW, WH, and HH growth were nearly identical among treatment groups. However, treatment differences present at 314 d persisted through 644 d, more than 10 mo after treatments ceased. These results suggested that protein during the early postweaning period and bST during the 200 to 300 d of age period just prior to puberty could be used to accelerate simultaneous increases in both BW and skeletal growth rates in dairy heifers without reducing age at puberty.