Effect of work applied at different stages of lactation on milk production, reproduction and live-weight change of F1 crossbred dairy cows used for draught
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Animal Science;69(pt. 3): 473-480
Permanent link to this item: http://hdl.handle.net/10568/28326
This study examined whether work applied at different stages of lactation had any effect on reproduction of cows under two feeding regimes. Twenty-four F1 crossbred dairy cows (12 Friesian X Boran and 12 Simmental X Boran) were allocated one of two diets (H + 3: natural pasture hay + 3 kg concentrate per day; and H + 5: natural pasture hay + 5 kg concentrate per day) and one of three work treatments - starting 45 days (D45), 90 days (D90) and 135 days (D135) post partum - using a principal component analysis score based on milk yield, live weight, calving interval and parity. Cows pulled sledges for 50 days (pull = 108 N per 100 kg live weight). Over the experimental period of 315 days, cows on diet H + 5 travelled a similar distance and produced amounts of fat-corrected milk (FCM) similar to those of cows on diet H + 3. Total intake of dry matter per kg live weight 0.75 was higher for cows on diet H + 5 than for cows on diet H + 3 and was similar across work times. Hay dry-matter intake was greater for the H + 3 group than for the H + 5 group at 180 days post partum and thereafter. Cows on diet H + 5 lost less weight in early lactation and gained more in mid and late lactation than cows on diet H + 3. During the work period, live-weight change was similar across diets but it was different between work treatments D45 and D135. The interval from calving to conception decreased by 63 and 101 days when start of work was delayed from D45 to D90 and from D45 to D 135, respectively. Output/input ratios of metabolizable energy equivalents were 0.35 for H + 3 and 0.37 for H + 5 diet, and 0.34, 0.37 and 0.40 for work times D45, D90 and D135, respectively. These results indicate that work started in early lactation significantly increased days to conception and decreased overall productivity of lactating working cows. Farmers must weigh the relative importance and cost of delayed ploughing against those of delayed oestrus or against the cost of borrowing draught power.