Food utilization by lactating dairy cows was studied in a randomized experiment covering the first 24 weeks of lactation, with further observations on performance over the remainder of the lactation under farm conditions. Over a 3-year period 90 firstcalf cows each took part in the experiment for one lactation, making six groups of 14-16 animals.For the experimental period a fixed basal diet was given of hay, concentrates, and wet brewer's grains. One group received only the basal ration. Four groups received in addition a fixed concentrates supplement for 4, 8, 12, 16 weeks from calving onwards respectively. The sixth group also had supplementary concentrates for 16 weeks but for weeks 5-12 inclusive the amount was doubled so that this group's diet simulated broadly ad libitum feeding in early lactation.Milk yield was increased by extra concentrates. The greater part of the effect was apparent in the first 2 weeks of different levels of intake, with a further build-up over the next 6-8 weeks. The size of the response fell as time from calving to initiation of different intakes increased. Additional food increased and delayed peak yield level. Persistency of milk yield was not affected by fixed differences in intake. Rate of liveweight change was improved by extra concentrates, less so in the third compared with the first month on treatment.A higher level of feeding in early lactation led to a greater partition of nutrients in mid-lactation to milk at the expense of gains in body reserves. This advantage to milk production extended to the end of lactation. In it the greatest response per unit concentrates was obtained from supplementation in the first 4 weeks of lactation but the total effect was increased by giving a double allowance of concentrates, and by extending the period of extra feeding to 8 weeks after calving.Solids-not-fat content and yield, and fat yield but not fat content, showed a similar response pattern to milk yield.Animal-to-animal variation in output on constant diets was characterized by negative regressions of live-weight change on milk yield. The regression coefficients were greater in early than in mid-lactation but they were constant in size at any one time for the various groups. A change in ration induced a change in output of the individual in which that production pathway favoured naturally by the animal was the more affected.

Seventy-six first-calf cows (heifers), 32 second-calf cows and 39 adult cows participated in a trial in which three diets composed of 60:40, 75:25, 90:10 proportions of compound to hay (hay dry-matter digestibility 0-6) were given for the first 36 weeks of lactation in amounts to provide daily an estimated 125, 156 MJ and ad libitum digestible energy (DE) for heifers, and 156, 187 MJ and ad libitum DE for the other parities. The ad libitum intakes were 150 and 200 MJ DE daily for heifers and for older cows respectively.Greater compound content of the diet and larger daily allowance of DE were associated with increased occurrence of mastitis and lameness but not digestive upsets. Dry-matter (D.M.) digestibility was increased with a greater proportion of compound in the diet but was not affected by the amount consumed or stage of lactation.Milk yield and live-weight change were increased linearly and additively by a greater intake of digestible dry matter and by a greater proportion of compound in the diet, throughout the lactation save for no effect of diet composition on live-weight change in early lactation. On equal feed intakes older cows gave more milk and lost more live weight than heifers in early lactation but not thereafter; responses to additional feed were equal for all parities studied.Milk fat concentration was reduced both by increased allowance and by the high compound diet. Milk solids-not-fat (SNF) concentration was not affected by the treatments. Yield of milk fat was not affected by amount eaten and was reduced by the 90:10 diet. Yields of SNF and milk energy were increased by amount eaten and by increased compound in the diet.Thirty-two primiparous cows continued on their experimental treatments without interruption to the end of the second lactation. In the second lactation the effects on yields of milk, milk energy, and SNF were magnified indicating a cumulative effect from lactation to lactation. Little cumulative effect was observed on either milk fat yield, or concentrations of fat and SNF in milk. More generous feeding was associated with reduced milk output/unit D.M. consumed in the first but not the second lactation. More generous feeding improved live-weight change less in the second than in the first lactation. No cumulative effects over two lactations were observed consequent upon variation in diet composition. INTRODUCTIONt a^e ' s u s u a^y achieved by increments of compound feeds/day, which simultaneously alters the diet Financial and physical constraints frequently composition); secondly the influence of parity of limit the size and scope of nutritional research on cow on performance; and thirdly the significance dairy cows, in the present context with regard to of the full lactation rather than a portion thereof input-output relationships, specifically plane of as the production period studied. Additionally, the nutrition. In consequence a large number of key rationing of cows according to individual current questionsremainunanswered.Amongstthesemaybe performance is being challe...

1. The results are reported of four feeding experiments in which lactating cows were given fixed rations of hay and high-cereal concentrates at different meal frequencies. In Expt 1 the total ration was given in two and twenty-four meals daily and in Expts 2 4 , the concentrates were given in two and five or six meals and the hay was given twice daily. The diets contained 600-900 g concentrate/kg.2. In all the experiments, more frequent feeding of these low-roughage diets reduced milk fat depression and increased milk fat yield. In each experiment the increase was greater with the diet containing the lower proportion of hay. There was no significant effect on milk yield, the protein or lactose contents of the milk or live-weight gain. Digestibility of dry matter, organic matter and energy was increased in one of the experiments but not in two others in which it was measured.3. More frequent feeding was calculated to increase the net energy secreted in milk and there was a tendency for it to increase the net energy in live-weight gain with diets containing 600 or 700 g concentrate/kg but to decrease it with diets containing 800 or 900 g concentrate/kg. These results are discussed in relation to theories of energy partition in lactating cows.4. It is concluded that at fixed feed intakes, the main response to increased meal frequency is likely to be a reduction in milk fat depression and that this will be confined to diets containing not more than about 200 g modified acid-detergent fibre/kg dry matter.

SummaryEight experiments, comprising four randomized-block feeding trials each with 20–45 animals and four changeover-design nitrogen (N) balance trials each with 6–10 animals, were used to study the effect of the addition of formaldehyde to fishmeal and to casein, of severe heating of fishmeal, and of tannin treatment of a mixture of vegetable protein-rich foods on the utilization of N for growth. Added in moderate amounts to rations demonstrated within the experiments to be deficient in N, quantities, but not the preparations, of N in the diet were critical to growth save at very low N intakes when the untreated foodstuffs were used more efficiently. Additional energy given in isonitrogenous rations increased growth, reducing N losses in the urine.

I. Sixteen first-calf Friesian heifers were used in a continuous treatment design experiment. For 2 weeks after calving they were given a 750 g concentrate, 250 g hay/kg ration with 169 g crude protein (nitrogen x 6.25; CP)/kg dry matter (DM). They were then divided into two groups of eight and given a high-protein (223 g CP/kg DM) or low-protein (107 g CP/kg DM) ration at the rate of 10.8 kg concentrates+ 3.6 kg hay for 8 weeks.2. Milk yield and composition, live weight and blood composition were monitored throughout. A digestibility trial was carried out with six animals on each treatment. 3.The low protein ration reduced DM, organic matter, energy and fibre digestibility significantly (P < 0.001) so that intakes of digestible energy were not equal and the low-protein group lost more weight than the highprotein group. 4.Milk yield and the fat content of milk were lower in heifers given the low-protein ration (P < 0.01). The lactose content of the milk was not affected and protein content only slightly reduced (P < 0.1) by lowprotein feeding. When the heifers were all changed onto an adequate protein (190 g CP/kg DM) ration in mid-lactation, those which had previously been under-fed protein appeared to recover in milk yield to the point they might have been expected to reach if given an adequate-protein ration throughout. 5.Concentrations of urea (P < o.001) and albumin (P < 0.05) were reduced by underfeeding protein, but albumin concentration was affected less by diet than by stage of lactation. Blood concentrations of total protein, glucose, sodium, potassium, calcium, inorganic phosphate, iron, copper, haemoglobin and packed cell volume were unaffected by treatment. Blood magnesium concentration was slightly lower (P < 0.1) with low-protein feeding.Few studies have been done, under UK feeding conditions, on the effects of low protein intakes on performance of cows early in lactation. This is a critical period in the lactation cycle when food intake often does not adequately match output of nutrients in milk, and body reserves of energy and possibly protein, are drawn on. Artificial manipulation (by abomasal infusion) of protein supply to cows in early lactation has prompted large responses i n milk nutrient output (0rskov et al. 1977) even to the extent that negative energy balance was increased.Only Treacher et al. (1976) have fed low-protein diets (down to ~2 0 g crude protein (nitrogen x 6.25; CP)/kg dry matter (DM)) to cows in early lactation in this country. They began low-protein feeding during gestation so that precalving and lactation effects were confounded.The effects of low-protein feeding in early lactation have received rather more attention in North America (Sparrow et al. We wished to study the gross effects of underfeeding of protein to heifers during the first 1 0 weeks of lactation by offering a ration containing less than I 10 g CP/kg DM. Where comparable levels of protein have been fed, the experiments have usually not been in early lactation and so may have been conducted in a less sensi...