Productivity of crossbred dairy cows suckling their calves for 12 or 24 weeks post calving.

An experiment on restricted suckling of crossbred dairy cows was conducted at the Livestock Research Centre, Tanga in northeast Tanzania. Thirty-six Bos taurus (Holstein Friesian and Jersey) x Bos indicus (East African Zebu) cows were allocated alternately as they calved to suckling their calves for either 12 or 24 weeks after calving. Cows grazed improved pastures and were offered 4 kg concentrate daily. Milking occurred twice daily by hand; calves were allowed to suck residual milk for 30 min following each milking. Calves were also allowed access to grazing and were offered a maximum of 1 kg concentrate daily to 24 weeks of age. Weaning age had no significant effect on lactation milk yield for human consumption, the mean (SE) yield being 1806 (102.0) L and 1705 (129.1) L for 12- and 24-week weaning, respectively. Cows from the two treatments suffered similar losses of live weight and body condition score during lactation and neither group had returned to the original body condition score 40 weeks following calving. Post-partum anoestrous intervals were prolonged. Although not significant, cows suckling calves to 24 weeks had a mean interval to first oestrus extended by 38 days compared with cows suckling calves to 12 weeks. The mean (SE) daily live weight gains of the calves to 52 weeks were 263 (14.1) g/day and 230 (18.1) g/day for calves weaned at 12 and 24 weeks, respectively, such that 12-month weights were 119 (5.6) kg and 110 (7.3) kg, respectively. Twelve-week-weaned calves consumed more concentrate (p<0.05) from 13 to 24 weeks than did 24-week weaned calves. Calculation of residual milk consumption removed by calves from birth to 12 weeks indicated that it accounted for 28%) of total yield. No benefits in cow and calf performance and welfare were found to justify prolonging the suckling period to 24 weeks.

Effect of restricted suckling of calves on the productivity of crossbred dairy cattle.

An experiment on restricted suckling of crossbred dairy cows was conducted at the Livestock Research Centre, Tanga in north-east Tanzania. The objective of the experiment was to evaluate the comparative productivity of Bos taurus x Bos indicus cows of medium and high levels of Bos taurus inheritance, whose calves were either bucket-reared or suckled residual milk. Lactation milk yield, length and persistency were 1563 L, 289 days, and 1.0, respectively, for the bucket-reared and 1592 L, 289 days and 1.4. respectively, for the suckling group. Days to observed ocstrus, first insemination and conception for cows whose calves were bucket-reared were 47, 74 and 115 days, respectively, and 57, 81 and 126 days, respectively, for the suckling cows. The calf weights were similar at 1 year of age. The productivity of the cows, measured as the annual milk offtake, was not significantly higher for those that suckled their calves than for those whose calves were bucket-reared.

Effect of environmental factors and of the proportion of Holstein blood on the milk yield and lactation length of crossbred dairy cattle on smallholder farms in north-east Tanzania.

A study was carried out on the lactation performance of crossbred dairy cattle in a smallholder farming system in north-east Tanzania. Data were collected from the records for 6 years and the factors considered were district, proportion of Holsteins, season of calving, year of calving and herd size. The data were considered separately for animals with a single lactation record. The least-square means for first lactation length and yield were 331 days (SD 77.0) and 2332 L (SD 283.0), respectively, while for cows with data on more than one lactation record the yield was 2477 L (SD 840.1) in 324 days (SD 74.0). First lactation yield was significantly affected by year of calving. For repeated records, the lactation yield was significantly affected by district, proportion of Holsteins and herd size, while lactation length was significantly affected by district and herd size. The calculated repeatabilities for lactation yield and length were 0.27 and 0.12, respectively. For the pooled data, the correlation between lactation length and yield gave r = 0.569 (p < 0.0001).

Influence of season of birth on weight for age in two genetic groups of cattle.

Body weights from birth to 756 days of age for calves of Mpwapwa cattle (12% Bos taurus inheritance) and backcrosses (34% Bos taurus) born in the wet or the dry season were analysed. The calves were weaned at 75 days of age and after that fed entirely on pasture. Backcrosses were heavier than Mpwapwa at birth and at 252 days of age but not at subsequent ages. Calves born in the dry season had slightly larger birth weights than calves born in the wet season. Weight differences were reversed from 252 to 504 days reflecting the seasonal fluctuations in grass growth. The effect of season of birth on long term rate of gain was negligible. No significant interaction between genetic group (Mpwapwa vs backcrosses) and season of birth (wet vs dry) was observed at any of the ages. The study thus did not confirm the hypothesis that backcrosses because of their higher proportion of Bos taurus genes were more sensitive to the nutritional stress of the dry season than were pure Mpwapwa calves.