Effects of bovine somatotropin on milk yield, mammary gland weight and histology in West African Dwarf goats

Twenty-four lactating West African Dwarf (WAD) goats were used to study the effects of bovine somatotropin (bST) on total milk yield (TMY), mammary gland weight and histology. The goats were equally assigned into four treatment groups, comprised six does each. The first group (control, T0) received no bST while the other groups received bST (T1, 20 mg; T2, 40 mg; T3, 60 mg) injected at 2-week intervals commencing from the 7th week postpartum for 6 weeks. The does were milked-dry twice daily by 7:30 a.m. and 7:30 p.m. respectively for 42 days commencing from the 7th to the 12th week of lactation. The yields were added to determine the daily milk yield (DMY) and the TMY was determined by cumulative daily milk yields for 42 days. At the end of twelfth week, twelve does (three from each treatment) were milked-dry by hand, slaughtered and their udders were excised. Udder weight (UW), Mammary gland weight (MGW) and volume (MGV) were determined. The effects of bST on mammary gland histology were investigated. The analyzed parameters included number of alveoli lobules (ALN), lactating alveoli (LA), regressing alveoli (RA), total alveoli (TA), alveolar corpora amylacea (ACA), interstitial corpora amylacea (ICA), total corpora amylacea (TCA), alveolar ductular diameter (ALD), epithelial luminal diameter (ELD) and epithelial height (EH). TMY was higher in treated goats and significantly (p<0.05) increased with increased doses of bST. UW, MGW and MGV were higher in treated than control goats suggesting that with advance lactation, bST administration maintains milk secreting cells. Treatment of lactating goats with bST significantly (p<0.05) increased the number of LA and significantly (p<0.05) reduced the number of RA, ACA and ICA. ALD, ELD and EH increased with increased doses of bST. ALD and ELD were significantly (p<0.05) larger and EH was significantly (p<0.05) higher in treated than control goats. Therefore, our findings suggest that the administration of bST to lactating WAD goats after peak of lactation appears to change mammary gland activity increasing milk yield. This is related to the maintained mammary glandular tissue weight resulting from increased lactating alveoli.