INFLUENCE OF DIETARY SUPPLEMENTATION AND PARTIAL SUCKLING ON BODY-WEIGHT AND ON LACTATION AND REPRODUCTIVE-PERFORMANCE OF PRIMIPAROUS BORAN(BOS-INDICUS) COWS IN ETHIOPIA

This study was conducted in the central highlands of Ethiopia during 1 990-92 to examine the effects of diet and partial suckling on lactatio n and reproductive performance of Boran (Bos indicus) cows. Primiparou s Boran cows were allocated to dietary supplementation or no supplemen tation with either milking or partial suckling based on body weight at calving. All cows received grass hay ad libitum and the supplemented groups were provided with additional concentrate feed which supplied 2 22 g/kg DM crude protein and 10 MJ/kg DM energy. Calves were weaned at 8 weeks of age. Mean (+/- S.E.) dam calving and calf birth weights we re 314 +/- 11.4 and 25 +/- 0.6 kg. Body weights at first postpartum oe strus and at conception were not affected by suckling. Supplemented co ws however, were heavier at first oestrus (P = 0.06) and at conception (P < 0.01) than non-supplemented cows. Lactation length was longer (P < 0.01) and mean daily milk yield higher (P < 0.001) in suckled than in milked cows. Diet, however, did not influence either lactation leng th or daily milk yield. In suckled cows, mean daily milk yield decline d sharply after weaning (week 9) and was lower by 38 and 43% of week 8 production in the supplemented and non-supplemented groups, respectiv ely. The overall mean lactation yield was 212.4 +/- 64.6 litres; with a significant (P < 0.05) diet x suckling interaction effect. Concentra tions of milk fat, total protein and total solids were not affected by either diet or suckling treatment. The postpartum anoestrus interval was longer (P < 0.01) in non-supplemented than in supplemented cows, b ut did not differ between suckled and milked cows. The percentage of c ows cycling by 150 days postpartum was higher (P < 0.05) in supplement ed than in non-supplemented and in milked than in suckled (P > 0.05) c ows. By this interval, a higher (P < 0.05) percentage of supplemented- milked (90%) cows cycled than in the other three treatment groups (48. 5%). Pregnancy from the first insemination ranged from 45.5 to 63.6% i n the four treatment groups. It was concluded that although partial su ckling extended the postpartum anoestrus interval, lactation length an d milk yield were improved. The negative effects of partial suckling o n postpartum reproduction could be overcome with the appropriate dieta ry supplementation. The economic trade-off between dietary supplementa tion, milk yield and reproduction has to be determined in partially su ckled cows.