The present paper discusses the results of a trial study, which was carried out to demonstrate the potential beneficial effects of virginiamycin (VM) on sow and litter performance. VM was added to the sow food at the levels of 0, 20 and 40 mg/kg, for a period of two breeding cycles, covering pregnancy and lactation. VM supplementation of the sow food improved sow performance by: (i) decreasing sow weight loss from farrowing to weaning (first period:decreasing the duration of the reproductive cycle (first period: 154-5 v. 152-2 v. 151-2 days, P < 0-05; second period: 153-8 v. 151-5 v. 250-6 days, P<0-05) and (in) increasing milk fat content (second period: 63-7 v. 81-3 v. 83-3 g/kg, P<0-05).Litter performance was also improved in terms of: (i) litter size at weaning (first period: 8-16 v. 8-88 v. 9-18, P < 0-05; second period: 8-98 v. 9-30 v. 9-76, P < 0-05), (ii) body weight at weaning (first period: 5-78 v. 6-29 v. 6-56 kg, P < 0-05; second period: 5-88 v. 6-38 v. 6-60 kg, P < 0-05), (Hi) average daily gain (first period: 172 v. 189 v. 197 g, P < 0-05; second period: 178 v. 292 v. 198 g, P < 0-05) and (iv) food conversion ratio (first period: 0-356 v. 0-331 v. 0-324, P < 0-05; second period: 0-363 v. 0-334 v. 0-325, P < 0-05). These beneficial effects of VM were more pronounced at the higher of the two inclusion levels.
EXPERIMENTALPreparation of the materials Freeze-dried cod muscle. This was cod muscle, i.e. fillets, that had been preheated in a commercial steam cabinet at 99' for 4-5 min, pressed to remove aqueous liquors, freeze-dried by an accelerated process and packed in cans under N,. In the laboratory, the resulting cod flake was hammer-milled to a coarse powder, gas-packed in ' oxygenfree' N, and held at -1 0 ' . (It was thus similar to the material used by Carpenter et al. (1957) except for the initial steaming and pressing.)One portion was reground to pass a 60-mesh sieve, then used for preliminary experiments in which small samples were heated in sealed glass ampoules. In the light of these results, certain heat treatments were selected and applied to the coarsely ground starting material in sealed cans in sufficient quantity for the main experiments, including animal feeding trials.Addition of glucose. When required a solution of D-glucose was added to cod-muscle powder in the proportion of either 5 parts glucose to 95 parts cod dry-matter or in the proportion of 10 to 90 parts respectively to form a slurry. After thorough mixing, the slurry was freeze-dried and reground. Adjzlstment of moisture content. A portion of the finely ground cod muscle was further dried by heating at greatly reduced pressure over P,O, for 24 h at 37' and then for 18 h at 7 0 ' . This material was used for studies of heating for 27 h at I 15' and for 729 h at 85". A second portion was dried, along with a sample of 'codfglucose' powder by standing over P,05 in an evacuated desiccator at room temperature for available at https://www.cambridge.org/core/terms. https://doi
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