The proportional hazards model with censoring was used to assess the effects of breeding value, disease, calving, size, and udder and lactation traits on length of herdlife of 3881 heifers in five herds. Data were recorded over 10 yr from three lines: a Holstein line, an Ayrshire-based line, and a crossbred line. Influences on survival were assessed from data collected at birth, 34, 50, and 82 wk, first freshening, and at 112 and 308 d postpartum. Median estimated herdlife (age at 50% culling) was 3.9 yr for animals alive at first freshening and increased to 4.3 yr for those that completed a first lactation (308 d postpartum). Herds differed greatly in the pattern of culling after freshening. Crossbred females had 21 wk longer median estimated herdlife than the mean of the purelines at 308 d postpartum. Individual milk yield was positively associated with longevity and had the greatest impact on length of herdlife. Abortion and fertility measured as days to last insemination were negatively associated with length of herdlife. Large heifers tended to have increased longevity. High feed intake postpartum was associated with reduced length of herdlife. Objective measures of conformation, which included measurements of the udder, were not important in determining herdlife.

Analysis of 3095 records from purebred and crossbred dairy cows at five research stations of Agriculture Canada showed that the additive, maternal, and heterosis effects on kind of birth, placental condition, and percent of male or female dead calves were of minor importance.

Data of 2779 purebred and crossbred heifers collected from five research stations of Agriculture Canada were used to study additive and nonadditive genetic effects on ages at first heat and at first breeding and conception rate at first service. Of these heifers, 2378 heifers had information on ages at first conception and at first freshening, days from first service to conception, and gestation length. The model included station, year of birth, sire, breed additive, maternal, and heterosis effects where sire effects were treated as random. Station differences were a significant source of variation for all reproductive traits. Year of birth had significant effects on four of seven reproductive traits. Breed additive effects for all genetic groups were not significant except for Finnish Ayrshire and American Holstein. No significant maternal effects were detected. Of 21 combinations of heterosis effects, six combinations showed significance. Partial regression coefficients ranged from negative to positive, suggesting that breed additive, maternal, and heterosis effects could increase or decrease for each percent increase of genetic contribution, depending upon the trait, breed group, and type of inheritance.

Holstein bull calves weaned at 5 wk of age were fed a complete calf starter ration with and without supplementation with soybean meal (SBM) or urea to provide the following levels of crude protein: (1) 12.5% (no supplement); (2) 17.5% (1.5% urea); (3) 21.6% (2.7% urea); and 17.9% (soybean meal). Calves fed the low protein starter had significantly poorer weight gains and feed conversion efficiency than those on the SBM starter; while feed intakes were only slightly reduced over the 8-wk experimental period. Calves fed the starters containing 1.5 and 2.7% urea had similar weight gains, feed intakes and feed conversion efficiency and their performance was intermediate between the low protein and SBM starter groups. Nitrogen retention was lowest with the low protein starter, tended to increase with increasing levels of urea and was highest when the starter contained SBM. Dry matter and energy digestibilities were lowest with the low protein starter, but were similar with the urea- and SBM-supplemented starters. There was no apparent advantage in increasing the crude protein content of urea-supplemented starters beyond 17.5%.

An experiment was conducted, using high selenium Record of Performance (ROP) test rations (0.46 and 0.78 ppm selenium), to study the effects of dietary supplementation with 0.1 ppm selenium (sodium selenate) on residues of the element in porcine tissues. Treatments included no selenium supplementation, selenium supplementation of the starter ration from 16 kg to 23 kg (average body weight), addition of selenium to both the starter and grower-finisher rations up to 57 kg, and dietary selenium supplementation for the entire starter-grower-finisher period. None of the treatments had any effects on the selenium content of kidney, liver, heart, blood, or loin, shoulder, and ham muscles, as compared with unsupplemented controls. The significance of the results is discussed in relation to differences in retention of natural dietary selenium and supplemental inorganic forms of selenium and likely effect of selenium supplementation of swine rations on selenium levels in the human diet.

Two types of sustained-release pellets (S.R.P.) were developed for administering chromium oxide (Cr2O3) to cattle and sheep: an extruded pellet (E.S.R.P.) for cattle, dissolution time 4 to 5 days, containing about 10 g Cr2O3, and a pressed pellet (P.S.R.P.), dissolution time 16 to 20 days, containing about 32 g Cr2O3 for cattle and 20 g for sheep and calves. Both types of pellets were retained by animals kept indoors and fed either long or chopped forage. Animals on pasture regurgitated 50% or more of E.S.R.P. and about 10% of P.S.R.P. Specific gravity of E.S.R.P. was 1.7 and of P.S.R.P., 2.8.Administration of Cr2O3 in S.R.P. eliminated the statistically significant diurnal excretion cycles normally observed with conventional once or twice daily dosing of animals in stalls. Small but statistically significant (P < 0.05) differences between grab samples of feces occurred with cattle on pasture grazed by free, strip, or mechanical (zero) systems.Sustained-release pellets are useful in experiments with animals kept in confinement but more general use is restricted because they cannot be made by commercial tabletting equipment and may be regurgitated by animals on pasture.

Four rations with the roughage consisting of silage alone, two-thirds silage and one-third hay, one-third silage and two-thirds hay, and hay alone, were fed to pregnant ewes during the three successive winter periods, 1955, 1956, and 1957. All groups received 0.9 lb. grain per ewe per day during the last 6 weeks prior to lambing.In 1957, when the dry matter content of the silage was only 21.4 per cent, the weight losses of the ewes were high and varied directly with the amount of silage fed. In 1955 and 1956, the weight changes were comparable to those in the hay-fed groups. Silage feeding had no effect on birth weights, 28-day weights, or weaning weights of the lambs, and ewe fleece weights were not affected.At birth 75 per cent of the lambs from the silage lots graded good or better, while 97 per cent of those whose dams were fed hay alone fell in these categories. Seventy per cent of the lambs born to silage-fed ewes survived to weaning compared with eighty-eight per cent of the lambs from the hay-fed group. Some of the ewes on grass silage lacked sufficient milk to support their lambs for a period of two weeks after lambing. T.D.N. intakes of the ewes on the rations containing silage alone and two-thirds silage, one-third hay were below the levels recommended in recognized feeding standards.