RESUMEN

Sixty medium-framed Hereford steers averaging 243 kg were used in an experiment including a growing period (28 wk) and a finishing period ending when the animals had approximately 4 to 10 mm of fat thickness (Canadian grade A1). Steers were assigned randomly to a 2 x 3 factorial arrangement of treatments for 28 wk (growing period). From the end of the growing period until slaughter, all steers received the same diet to study the residual effect of treatments fed during growth. Treatments during the growing phase consisted of two types of forage conservation (silage or hay) and three levels of protein supplement (0, 200 g of fish meal plus 43 g of urea, or 400 g of fish meal). There was an interaction (P less than .05) between forage conservation and protein supplementation for BW gain during the growing phase; the greatest gain was by steers fed silage and 400 g of fish meal (.87 kg/d). There was no difference in BW gain among animals fed the hay diets, which averaged .75 kg/d. Body weight gain during the finishing phase, and for the overall experiment, was affected only by forage conservation; greater gains were made by steers fed silage during the growth phase. Protein supplementation did not affect performance in either the finishing phase or overall. Carcass composition did not differ among treatments, and time spent on the finishing phase tended to be less (P less than .08) for steers fed silage plus 400 g of fish meal during the growth phase.

Asunto(s)

RESUMEN

Six Hereford steers averaging 256 kg were used in a 2 x 3 factorial arrangement within a 6 x 6 Latin square design to study the effect of forage conservation (silage vs hay) and N supplementation (0, 200 g of fish meal plus 43 g of urea, or 400 g of fish meal) on ruminal characteristics, digestibility, blood urea, and in situ degradability of DM, N, and ADF. Dry matter intake of forage and total DMI did not differ among treatments (P greater than .05) and averaged 5.3 and 5.5 kg, respectively. Steers fed silage had greater (P less than .05) pH and concentrations of ammonia N, isobutyrate, isovalerate, and valerate in the rumen than in the rumen of those fed hay. Nitrogen supplementation increased (P less than .05) concentrations of total VFA and valerate in the rumen. Digestibility of N and ADF was greater (P less than .05) for silage than for hay, and N supplementation increased digestibility of N. Plasma urea concentrations were greater (P less than .05) for steers fed silage than for those fed hay. These data suggest that feed utilization is better with silage than with hay and is increased by N supplementation.

Asunto(s)

RESUMEN

Ninety multiparous Holstein cows were used to measure the effect of energy during the prepartum and postpartum periods. During the prepartum period (63 d) half of the cows were fed grass silage ad libitum and a concentrate (16% protein) was offered daily at .25% of BW. The other half of the cows were offered the silage ad libitum but concentrate at .75% of BW. At calving each of the two prepartum groups was subdivided into three subgroups and fed corn silage for ad libitum consumption, 4.5 kg of hay/d and concentrate (20% protein) at .25 or .75% of BW daily, or ad libitum. After 112 d of lactation, all cows were switched to a diet consisting of corn silage fed ad libitum and 1 kg of concentrate (20% protein)/4 kg of milk. Roughage intake was reduced with an increase of concentrate consumption. Body measurements, calf weight, milk yield, feed efficiency, services per conception, and incidence of diseases were not influenced by the prepartum regimen. However, the interval from parturition to conception was 24 d longer for cows on the higher prepartum energy concentration (.75% of BW). None of the cows was able to meet its nutrient requirement in early lactation. Milk yield increased with each increment of concentrate in the postpartum diet. Reproduction and health were not affected by the postpartum regimen.

Asunto(s)

RESUMEN

Changes in follicular development of the ovary at 105, 140 and 175 d of age were observed on 48 prepuberal Yorkshire and Hampshire gilts raised on two planes of nutrition. The follicles from the left ovary were counted and measured by histological techniques. Both the nonatretic and the atretic (more than four pyknotic bodies) antral follicles were classified into six categories according to size, and each category was expressed as percentage of the total number. The proportion of nonatretic follicles belonging to the first category (.19 to .36 mm in diameter) was higher in Hampshire than Yorkshire gilts at d 105 (65.4 vs 47.6%; P less than .05), but not at d 140 and 175. The proportion of atretic follicles to the total number observed was higher in Yorkshire at d 175 than at d 140 and 105 (38.6 vs 21.9 vs 11.6%, respectively; P less than .05), whereas in Hampshire, significant differences were observed only between d 140 and 105 (25.2 vs 3.9%, respectively). The low-plane regimen reduced the percentage of nonatretic follicles of the third (.63 to 1.12 mm) and fourth (1.13 to 2.00 mm) categories in Yorkshire gilts from 14.4 and 7.2% to 9.7 and 4.0%, respectively (P less than .05). According to grouping, size and number of antral follicles, three morphological types of ovaries could be distinguished: honey-comb, grape-like and an intermediate class. Reanalyzing the data accounting for types resulted in radical reduction in the residual variation, hence many significant differences between the two breeds could be identified. At 140 and 175 d of age, Hampshires with honey-comb- and grape-like ovaries had greater numbers of medium and large follicles than Yorkshires (P less than .001). It is concluded that the slower follicular development observed at 105 d of age in Hampshire, as compared with Yorkshire gilts, allows accumulation of greater numbers of antral follicles at 140 and 175 d for both morphological types of ovaries.

Asunto(s)

RESUMEN

Forty female and ten male pigs were used to study the effect of carbadox on reproductive performance when included in the diet at a level of 55 mg/kg from one week of age through approximately 60 kg body weight. Five replicates, each consisting of eight females and a pair of littermate boars, all crossfostered, were used. One boar reared on medicated feed and another on an unmedicated diet, were bred to two groups of four littermates. One female in each pair had been fed the medicated diet, and the other the unmedicated diet. The same breeding scheme was carried out for two parities. The following observations were made: length of estrous cycle, weaning-to-estrus interval; conception rate; age and weight at first estrus, at breeding, at 109 days of gestation, at farrowing and after farrowing; gestation length; and litter size and weights at birth and 28 days. The results showed that carbadox had no apparent effect on reproductive performance.