Effect of work applied at different stages of lactation on milk production, reproduction and live-weight change of F-1 crossbred dairy cows used for draught

This study examined whether work applied at different stages of lactation h ad any effect on reproduction of cows under two feeding regimes. Twenty-fou r F-1 crossbred dairy cows (12 Friesian X Boran and 12 Simmental X Boran) w ere allocated one of two diets (H + 3: natural pasture hay + 3 kg concentra te 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 13 5 days (D135) post partum - using a principal component analysis score base d on milk yield, live weight, calving interval and parity. Co sus pulled sl edges for 50 days (pull = 108 N per 100 kg live weight). Over the experimen tal 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 d iet 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 w ork times. Hay dry-matter intake was greater for the H + 3 group than for t he H + 5 group at 180 days post partum and thereafter. Cows on diet H + 5 l ost less weight in early lactation and gained more in mid and late lactatio n than cows on diet H + 3. During the work period, live-weight change was s imilar across diets but it was different between work treatments D45 and D1 35. The interval from calving to conception decreased by 63 and 101 days wh en start of work was delayed from D45 to D90 and from D45 to D 135, respect ively. Output/input ratios of metabolizable energy equivalents were 0.35 fo r 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 ea rly lactation significantly increased days to conception and decreased over all 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.