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The influence of sex and gonadectomy on liveweight growth and its components was examined in a comparative slaughter experiment using Southdown – Romney cross lambs run under New Zealand pastoral feeding conditions.Twenty ram lambs were castrated and 20 ewe lambs spayed at docking, at approximately 4 weeks of age. Ten ram and 10 ewe lambs were killed at this age and 5 lambs from each of the four ‘sexes’ (entire and gonadectomized, male and female) were killed 4, 8,12 and 24 weeks after docking.Live-weight gain was higher for males than females and higher for entire than gonadectomized lambs, with some evidence of a greater depression in growth associated with castration than spaying. Effects on carcass weight followed those on live weight; weights for entire rams, wethers, entire and spayed ewes were 16.92, 14.72, 14.02 and 12.46 kg. respectively at approximately 7 months of age.

No abstract

Factors associated with mortality in 7,727 lambs born to 7,091 twoto five-year-old ewes over the 9 years 1959-67 were studied. The lambs were from two Romney flocks and first-, second-, third-, and fourthcross Border Leicester x Romney flocks. Lamb survival rate (lambs weaned as a percentage of all lambs born) increased with increasing age of dam for both single-and multipleborn lambs. Variation in survival rate between flocks and between female and male lambs was large. In 60% of the dead lambs, 44.6% of single-born lambs died of dystokia and 15.1 % from physiological starvation. Of the multiple-born lambs autopsied, 16% died from dystokia and 41.7% from starvation. Infections accounted for 11.6% and pre-natal deaths for 10.3% of the remaining deaths. Most of the deaths occurred within 3 days of birth, and relatively more single-than multiple-born lambs died at birth. Analysis of variance of birth weight showed that first-cross lambs were the heaviest and that birth weights decreased with interbreeding, to the fourth-cross lambs. Male lambs were 0.5 Ib heavier than females and singles 2.3 Ib heavier than twins. Lamb birth weight increased from two-year-old to five-year-old dams. Survival rate was related to birth weight. In single-born lambs survival rate was highest in lambs of about average birth weight and decreased with lambs of lower or higher birth weights. In multipleborn lambs survival rate was lowest with lambs of low birth weight and increased with increasing birth weight. Lamb mortality was highest in the earliest-born lambs.

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Data are reported on the calving performance of cows in beef production trials in three successive calvings of South Auckland herds. The main comparison of Friesian, Hereford, and Charolais sires over the Jersey cow is supplemented by information on the Friesian cow mated to these three sire breeds and on straightbred Jersey and straightbred Angus calvings.Overall, 81% of ca1vings were unobserved. Eight percent of all ca1vings, or 45% of observed calvings, were assisted. Jersey and Friesian cows required more assistance when calves were sired by Charolais and Friesian sires, and least when Hereford sires were used.Cow mortalities at calving time were greatest for Jersey and Friesian cows in-calf to Charolais sires. Perinatal calf mortalities accounted for 3.5% of all calves born, with a greater mortality of calves by Charolais sires than other breeds.Calves assisted at birth were heavier than those from unassisted calvings, but gestation lengths did not differ significantly. Calves dying at birth had a shorter gestation period and were lighter than surviving calves.There were significant sire and farm effects on birth weight and gestation length of Jersey crossbred calves, and age of dam significantly affected birth weight but not gestation length. Bull calves had longer gestation periods and were heavier at birth than heifers. Sire breed affected calf birth weights in the descending ranking order of Charolais, Friesian, Hereford, and Jersey. Purebred Angus calves were similar in birth weight to Hereford X Jersey crossbreds. Friesian cows produced heavier calves than Jersey cows. Gestation periods were longest for calves with Charolais sires; those sired by the Hereford were next longest; and Friesian and Jersey sire breeds had the shortest gestations.Heritabilities of birth weight and gestation length were calculated as 0.31 and 0.12 respectively.Results are discussed in relation to beef breeding programmes.

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The influence of sire and age on the palatability characteristics of rib-loins from Southdown X Romney lambs was studied. Twelve lambs were selected from each of six Southdown sire groups, and one-third of these lambs were slaughtered at 17, 22, and 27 weeks of age respectively. Neither taste panel nor tenderometer detected any over-all effect due to sire on tenderness, and panel scores for texture, juiciness, and flavour of cooked meat did not vary significantly between sires. Both the taste panel scores and the tenderometer values showed that older lambs were less tender than younger lambs. The results indicated that the fatness of the lamb carcass had no influence on the tenderness of the meat.