SUMMARYThirty-six mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used in a comparative slaughter experiment to measure changes in body tissues during early lactation. Two levels of body fatness at lambing were established by giving ewes a complete diet containing 10 MJ metabolizable energy (ME) and 139 g crude protein (CP)/kg d.m. either close to requirements or ad libitum during the second half of pregnancy. In lactation half the ewes in each group were given a complete diet containing either 90 (diet A) or 60 (diet B) % milled hay ad libitum. These diets contained 7·9 and 9·2 MJ ME and 121 and 132 g CP/kg d.m. respectively.Ewes fed at the two levels in pregnancy contained 8·4 and 19·6 kg chemically determined fat 5 days after lambing but had similar amounts of body protein, ash and water. Over 6 weeks of lactation ewes given diet A lost 60 and 69% of these weights of fat respectively, while ewes given diet B gained 5% and lost 30% respectively. Up to 26 g of body protein was lost daily from ewes given diet A but none from ewes on diet B. During early lactation the weight of the empty digestive tract increased while the weights of most other body components, particularly the carcass, decreased. The ratio of body energy change to live-weight change varied from 24 to 90 MJ/kg. Thus live-weight change did not accurately reflect relative or absolute changes in body energy.Voluntary food intake was greater for ewes given the high-energy diet (B) than for those given diet A and was depressed in the fatter ewes. Differences in intake could be explained by the effects of body fatness and diet on the weight of gut contents. Milk yield was not significantly affected by body fat reserves but was higher on diet B than A. Fat content of milk was higher and protein content lower for ewes with the higher fat reserves at lambing.As the contribution of fat loss to energy available for milk synthesis increased there appeared to be a reduction in the energetic efficiency of milk synthesis. A number of possible reasons for this are discussed.

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Changes in body composition during lactation were measured in 12 Border Leicester x Scottish Blackface ewes by serial slaughter at 12, 41 and 111 days of lactation. Ewes suckled twin lambs and were given daily 1-6 kg dry matter of a complete diet containing 151 g crude protein and 10-2 MJ metabolizable energy/kg dry matter. Live weights of ewes averaged 60-2, 58-9 and 55-8 kg at 12, 41 and 111 days of lactation respectively. There were no significant changes in weights of stomach, small and large intestine and liver. The weight of body fat averaged 9-19, 2-28 and 1-19 kg at 12, 41 and 111 days respectively (P< 0-001) and weight of ash increased from 1 -72 kg at 12 days to 2-30 kg at 111 days (i> < 0-001). Water to protein ratios at the three stages of lactation were 2-94, 3-36 and 3-18 (/ > <0-10). The energy value of weight loss varied from 68 to 17 MJ/kg, depending on the relative changes in total body water and fat. Live-weight change was therefore a poor indicator of change in body energy during early lactation. Body fat could be predicted from its combined relationships with live weight and total body water (residual s.d. ± 0-70 kg), but when deuterium oxide space was used to estimate body water separate equations were necessary for early and later stages of lactation. This was apparently due to differences between stages of lactation in the time required for deuterium oxide to equilibrate with water in the reticulo-rumen.

SI'MMARY. Thirty-nine British Friesian cows and 17 British Friesian heifers were used to measure the effects on milk yield, food intake and digestion, and N balance of increasing the protein concentration in the diet from 111 to 147 g crude protcin/kg dry matter during the first 16 weeks of lactation. The comparison was made for animals given food either ad lib. or at a level which allowed them to gain 05 kg/d during the 8 weeks before parturition, and for animals given ad lib. diets of either 60:40 or 40:60 hay: concentrate ratio during early lactation. Milk yield was increased by a higher protein concentration in the diet (/-* < 001) and the increase was evident from the first week of lactation. Mean increases over the first 8 weeks of lactation were 3 kg/d for animals on the diet of high roughage content and 7 kg/d for animals on the diet of low roughage content. A higher crude protein content in the diet also increased food intake (P < 0 -05) and digestion (P < 0 -05), and the increases were greater for animals given the diet of low compared with high roughage content. Level of feeding before parturition did not influence food intake or milk yield and there were no differences between cows and heifers in their response to treatments. N balance over the first 10 weeks of lactation averaged -13 g/d for cows and 6 g/d for heifers (P < 0-025). and was not significantly altered by treatments. Mean N balance of all animals was estimated to increase from -37 g/d immediately after parturition to zero at 8 weeks of lactation. The results demonstrate that an increased protein concentration in the diet during early lactation is associated with increased food intake and digestibility of food, which are in turn largely responsible for higher levels of milk production.

An experiment using herds of ~20 cows (farmlets) assessed the effects of high stocking rates on production and profitability of feeding systems based on dryland and irrigated perennial ryegrass-based pastures in a Mediterranean environment in South Australia over 4 years. A target level of milk production of 7000 L/cow.year was set, based on predicted intakes of 2.7 t DM/cow.year as concentrates, pasture intakes from 1.5 to 2.7 t/cow.year and purchased fodder. In years 1 and 2, up to 1.5 t DM/cow.year of purchased fodder was used and in years 3 and 4 the amounts were increased if necessary to enable levels of milk production per cow to be maintained at target levels. Cows in dryland farmlets calved in March to May inclusive and were stocked at 2.5, 2.9, 3.3, 3.6 and 4.1 cows/ha, while those in irrigated farmlets calved in August to October inclusive and were stocked at 4.1, 5.2, 6.3 and 7.4 cows/ha. In the first 2 years, when inputs of purchased fodder were limited, milk production per cow was reduced with higher stocking rates (P < 0.01), but in years 3 and 4 there were no differences. Mean production was 7149 kg/cow.year in years 1 and 2, and 8162 kg/cow.year in years 3 and 4. Production per hectare was very closely related to stocking rate in all years (P < 0.01), increasing from 18 to 34 t milk/ha.year for dryland farmlets (1300 to 2200 kg milk solids/ha) and from 30 to 60 t milk/ha.year for irrigated farmlets (2200 to 4100 kg milk solids/ha). Almost all of these increases were attributed to the increases in grain and purchased fodder inputs associated with the increases in stocking rate. Net pasture accumulation rates and pasture harvest were generally not altered with stocking rate, though as stocking rate increased there was a change to more of the pasture being grazed and less conserved in both dryland and irrigated farmlets. Total pasture harvest averaged ~8 and 14 t DM/ha.year for dryland and irrigated pastures, respectively. An exception was at the highest stocking rate under irrigation, where pugging during winter was associated with a 14% reduction in annual pasture growth. There were several indications that these high stocking rates may not be sustainable without substantial changes in management practice. There were large and positive nutrient balances and associated increases in soil mineral content (P < 0.01), especially for phosphorus and nitrate nitrogen, with both stocking rate and succeeding years. Levels under irrigation were considerably higher (up to 90 and 240 mg/kg of soil for nitrate nitrogen and phosphorus, respectively) than under dryland pastures (60 and 140 mg/kg, respectively). Soil organic carbon levels did not change with stocking rate, indicating a high level of utilisation of forage grown. Weed ingress was also high (to 22% DM) in all treatments and especially in heavily stocked irrigated pastures during winter. It was concluded the higher stocking rates used exceeded those that are feasible for Mediterranean pastures in this environment and upper levels of stocking are suggested to be 2.5 cows/ha for dryland pastures and 5.2 cows/ha for irrigated pastures. To sustain these suggested stocking rates will require further development of management practices to avoid large increases in soil minerals and weed invasion of pastures.