Lamb Mortality in Hill Country Flocks

G.K. Hight and K.E. Jury

Whatawhata Hill Country Research Station

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Proceedings of the New Zealand Society of Animal Production. 1969, 29: 219-232

The factors associated with lamb mortality in 7,727 lambs born to 7,091 two-tooth to four-year-old ewes over the 9-year period 1959-67 were studied. The lambs (from six flocks) were Romney (two flocks) or first-cross (F₁), second-cross (F₂), third-cross (F₃), and fourth-cross (F₄), Border Leicester x Romney sheep. Data are presented of the effects of flock, age of dam, lamb sex, birth rank, mortality characteristic, age at death and birth weight on survival rate (lambs weaned as percentage of all lambs born). The overall survival rate was 82.2%.

Survival rate for single-born lambs was highest from six-tooth ewes, and in multiple-born lambs from four-year-old ewes. Mortality of twin lambs was higher than for singles. Year of birth had a marked effect on survival rate, with the variability in survival rate between years being greater for multiple- than single-born lambs.

Female lambs had a higher survival rate than castrated male lambs, the overall difference in lambs weaned as a percentage of lambs born being 5.8. Within sexes and birth rank, survival rate increased from the Romney to F₂ lambs and then declined with interbreeding to the E and F, Iambs. This indicates that maternal and/or heterosis effects influenced lamb mortality.

On a 60% sample of the dead lambs only, 44.6% of single lambs died of dystokia, and 15.1% from physiological starvation. In the sample of multiple-born lambs autopsied, 16% died from dystokia and 41.7% from starvation. Infections accounted for 11.6%, and prenatal deaths for 10.3% of the remaining deaths. Most of these deaths occurred within 3 days of birth, with relatively more single- than multiple-born lambs dying at birth.

The survival rate of single- or multiple-born lambs 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 multiple-born lambs, survival rate was lowest with lambs of low birth weight and increased with increasing birth weight.

Keywords: NZSAPAB;

Last Updated 24-08-2000