SEASONAL EFFECTS ON GESTATION LENGTH AND BIRTH-WEIGHT IN ALPACAS

Gestation lengths and birth weights were measured in 162 pregnancies i n alpacas (Lama paces) farmed in the high country of the South island of New Zealand. A comparison of pregnancies from spring (mid-October t o mid-December) and autumn (mid-February to late April) matings showed that gestation lengths were 12.5 days longer in spring (348.9 +/- 1.4 days vs. 336.4 +/- 1.2 days; P < 0.0001). For each day later in sprin g that a female was mated there was an increase in gestation length of 0.11 days (P < 0.05), whereas for each day later in autumn the gestat ion was reduced by 0.24 days. There were no significant effects of sex of cria or age of dam on gestation length. After adjustment for gesta tion length, crias born in autumn weighed 1.0 kg more than those born in spring (8.8 +/- 0.15 kg vs. 7.8 +/- 0.18 kg; P < 0.001). Female cri as weighed 0.4 kg less than males at birth (P < 0.05). The results sug gest that in this environment it will be difficult to maintain spring- mated females in a 12 month breeding cycle. (C) 1997 Elsevier Science B.V.