Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/14/2003
Publication Date: 11/1/2004
Citation: Capuco, A.V., Dahl, G.E., Wood, D.L., Moallem, U., Erdman, R.E. 2004. Effect of bovine somatotropin and rumen undegradable protein on mammary growth of prepubertal dairy heifers and subsequent milk production. Journal of Dairy Science. 87(11):3762-3769. Interpretive Summary: Rapid body growth during the prepubertal period may be associated with reductions in mammary parenchymal growth and subsequent milk yield. The objectives of this study were to determine the effects of dietary rumen-undegradable protein (RUP) and administration of bovine somatotropin (bST) during the period from weaning until puberty on mammary growth and milk production of Holstein heifers. Growth of mammary secretory tissue was assessed by change in mass and histological evaluation of markers for cell proliferation. Mammary growth was not affected by RUP or bST treatment. Although we demonstrated that dietary RUP and bST administration accelerated body and skeletal growth rates, there were no deleterious effects on prepubertal mammary gland growth. Subsequent milk production and composition were also equivalent for all treatment groups. Data suggest that incorporation of dietary RUP and bST administration into an accelerated heifer-rearing program can provide for larger framed heifers without associated loss of milk production or increased calving difficulty.
Technical Abstract: Rapid body growth during the prepubertal period may be associated with reductions in mammary parenchymal growth and subsequent milk yield. The objective of this study was to test effects of dietary rumen undegradable protein (RUP) and administration of recombinant bovine somatotropin (bST) during the prepubertal period on mammary growth and milk yield of dairy heifers. Seventy-two Holstein heifers were used in the experiment. At 90 d of age, eight heifers were slaughtered prior to initiation of treatment. The remaining heifers were randomly assigned to one of four treatment groups. Treatments consisted of a control diet (5.9% RUP, 14.9% CP, DM basis) or RUP-supplemented diet (control diet plus 2% added RUP) with or without 0.1 mg of bST/kg BW/d applied in a 2 x 2 factorial design. A total of six heifers per treatment group (3 each at 5 and 10 mo of age), were slaughtered for mammary tissue analysis. The remaining heifers were bred to evaluate impact of treatment on milk yield and composition. Mammary parenchymal growth was not affected by RUP or bST treatment. Total parenchymal mass increased from 16 g to 364 g, and parenchymal DNA from 58 mg to 1022 mg from 3 mo to 10 mo of age, respectively. Furthermore, the number of mammary epithelial cells likely was not affected by diet or bST because the epithelial cell proliferation index, assessed by Ki-67 labeling, was not affected by treatment, nor was total parenchymal DNA and lipid content. Although we demonstrated that dietary RUP and bST administration accelerated body and skeletal growth rates, there were no deleterious effects on prepubertal mammary gland growth. Subsequent milk production and composition was equivalent for all treatment groups.