Two experiments were carried out to measure effects of body condition at calving and different levels of feeding after calving on milk and subsequent reproduction.In experiment 1, which was conducted in two consecutive years, 162 cows (77 in year 1 and 85 in year 2) were group feed so as to reach a target body condition (condition scores ranging from 3-6) four weeks before calving. During the last four weeks before calving, all cows were managed so as to maintain their individual condition scores. At calving, cows in similar condition of similar breed and with similar previous milk production were allocated to high and low levels of feeding at pasture for the first five weeks of lactation. Mean pasture intakes were 13.0 and 7.0kg dry matter (DM)/cow.d in year 1 and 15.0 and 8.5 kg DM/cow.d in year 2In experiment 2, 40 cows were offered pasture and hay from 20 weeks before calving to achieve a body condition score of either 4 or 6 by two weeks before calving. During the first five weeks of lactation, cows were individually fed in stalls on freshly cut pasture at one of three levels of intake, 7 or 10 kg DM/cow.d or .In both experiments cows were grazed as one group from week 6 to 20 of lactation.Improved body condition at calving resulted in an extra 4.0, 11.0 and 7.4 kg milk fat per unit condition score over 20 weeks of lactation, for year 1 and 2 of experiment 1, and experiment 2, respectively. Cows in poorer condition partitioned a higher proportion of feed energy to liveweight at the expense of milk production than did the cows in better condition. However, increasing the plane of nutrition in early lactation resulted in higher levels of milk production and reduced the need for cows to mobilize bodyreserves. Improved body condition at calving had a positive effect on milk fat percentage, particularly in early lactation, but did not affect milk protein percentage. Input-output relations calculated from the experimental data showed that the benefit sf to improve body condition before calving was less than that of additional feeding after calvin changes in the condition of the cows were taken into consideration (25.8 vs 1 4.6 kg DM to yi kilogram of milkfat). Improvements in condition and feeding in early lactation reduced the anoestrus interval after calving by 5.7 d for each additional condition score at calving and 1. d for each additional kgDM/cow.d fed over weeks 1-5 of lactation. The input-output relations resented will enable farmers to assess the likely consequenes of changes in their feeding management in the crucial peripartum period with a greater degree of confidence than in the past.
Eighty cows of mixed breeds were fed so that they calved in moderate condition, and were then strip-grazed at different rates over the first ten weeks of lactation. Two levels of feeding were used factorially ; either ad libitum pasture intake (H) or an allowance of pasture which resulted in an intake of 7 kg of pasture dry matter cow-1 day-1 (L), for the first or second five-week period. After ten weeks, all cows were grazed as one group as well as seasonal conditions permitted. The effects of five-week periods of underfeeding on milk, milk fat and protein yield were equal and additive over the first ten weeks of lactation, HL and LH groups producing 11 kg and LL group 22 kg less milk fat than the HH group. Residual effects, however, from week 11 to the end of lactation differed markedly between treatments, the LH group producing the same as, but HL and LL groups producing 9 and 21 kg less than, the HH group. Residual effects of only 0.7 and 1.0 times the immediate effect were recorded for underfeeding in the first five and ten weeks of lactation, respectively. Cows underfed in early lactation gained more liveweight in later lactation at the expense of milk yield. An extra 10 kg pasture dry matter was required in early lactation to give an extra kilogram of milk fat over the lactation. The calving to conception interval in the LL group was 18 days longer than in the HH group (P < 0.05). The delay was associated with both a longer post-partum anoestrus and a higher number of services per conception. There was no effect of stage of underfeeding (HL vs LH) on reproductive performance. The poor understanding of factors affecting residual effects from underfeeding in early lactation is highlighted. As pattern of underfeeding has little effect on lactation performance, this gives the farmer considerable flexibility in allocating feed supplies in early lactation.
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