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Seventy-seven cows of mixed breeds were allocated a range of pasture only or pasture/hay diets for the first 60 days of lactation. The variation in level of pasture intake was achieved by stripgrazing. The average in vitro dry matter digestibility and nitrogen content of the pasture offered was 72.0 and 3.11 % respectively, while those of the hay were 63.3 and 2.24%. The pasture alone treatments examined the effects of underfeeding on dairy cow productivity and the pasture/hay treatments established the extent to which these effects could be overcome by the use of hay as a supplement to limited pasture. After 60 days, all cows were grazed as one group at a stocking rate of 6.0 cows ha-1. Underfeeding in the first 60 days of lactation resulted in a loss of 68.3 kg milk/cow for each kg reduction in daily pasture intake, together with a decline in liveweight and body condition. When hay was offered as a supplement, it overcame the effects of underfeeding to a large extent although milk production still declined by 31.3 kg/cow for each kg reduction in daily pasture intake. There was a residual loss in milk production of 0.6 times the immediate loss for 60 days of underfeeding. The residual benefit gained from feeding hay at any level of underfeeding averaged 0.5 times the immediate benefit. Hay was unable to counteract completely the effects of underfeeding because its nutritive value for production was only half that of pasture, and the cows could not eat enough of it to overcome this. Some possible variations to these results are considered, taking into account the quality of the pasture and hay used. The economic use of hay as a supplement to limited pasture is discussed. Providing hay is used as a genuine supplement, the use of it will be economic as long as the cost of a kg of hay is less than the price paid for 0.049 kg butterfat. The limitations to this calculation are discussed. |
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