1. One-hundred-and-ten British Friesian, British Friesian x Ayrshire or successive backcrosses to British Friesian heifer calves were allocated to three groups. Groups A and B were rapidly reared and fed a barley-beef diet which resulted in mean body-weight gains exceeding 1 kg/day (13 to 39 weeks) and group C was normally reared on summer grazing and hay plus concentrates in winter at a mean bodyweight gain never exceeding 0-74 kg/day. Animals in group A were first mated at an average age of 42-9 weeks (body weight, 302 kg). Groups B and C were mated later at average ages of 78-4 and 78-1 weeks (average body weights, 443 and 353 kg respectively). After the first calving all animals were fed and managed as a single group. 2. There were no significant differences between the proportion of heifers conceiving at first service in groups A (55-5%), B (66-7%) and C (72-4%). 3. There were no differences in the incidence of dystocia at first calving in heifers served by an Aberdeen Angus bull but 12 out of 19 heifers in group A served by a British Friesian bull had dystocia. 4. Average 305-day fat-corrected milk yields in the first four lactations in group A (18 animals) were 1959, 2918, 3545 and 3210 kg and in the first three lactations in group B were2450,3216and3310kgand in group C 3863,4694 and 4813 kg. Thus milk yield was significantly lower in all lactations for rapidly-reared animals irrespective of the age at breeding and was further significantly lowered in the first lactation of animals mated early. 5. There was a high incidence of laminitis and bloat in heifers reared on the barley-beef diet, but during lactation, there was a lower incidence of mastitis in the lower-yielding, rapidly-reared groups.
Two diets containing reduced levels of crude protein for both growing (35-65 kg) and finishing (65-95 kg) pigs were tested against standard commercial diets to determine changes in the odorants produced in fresh slurry. The experimental diets were formulated on a least cost basis using either a full commercial database or with restriction mainly to home-grown (UK) cereals and pulses. Synthetic essential amino acids were included in both formulations to obtain essential amino acids in an ideal protein ratio, with the crude protein being as low as possible. Nitrogen excretion by both growing and finishing pigs offered the low crude protein diets was significantly lower ( P < 0.001) than that of pigs offered the commercial diets. Major odorants responsible for pig odour from slurries were identified and their concentrations determined using gas chromatographymass spectrometry. Five out of 10 odorants from slurries produced by growing pigs were significantly lower ( P < 0.05) in concentration for each of the low crude protein diets compared with the commercial diet. For the finishing pigs, nine out of ten odorants from slurries for the least cost and four odorants for the home grown diets were significantly lower ( P < 0.05) than slurry produced from the commercial diet. Reducing dietary nitrogen and providing essential amino acids in an ideal protein ratio not only decreases the nitrogen excreted by the pig, but also reduces odorants produced in the resultant slurries.
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