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Influence of aridity on reproduction of the collared peccary (Dicotyles tajacu (linn)) in Texas Low, William A


Reproduction and productivity of the collared peccary, Dicotyles tajacu angulatus, were examined in Texas under moist and draught conditions, and in captivity under presumed optimal conditions. Foetal sex ratios favour females, but change to favour males shortly after birth, and again favour females in the older age classes. The south Texas population contained a higher proportion of older animals than the west Texas population. Life expectancy at 1 year of age was estimated at 3.0 years in south Texas peccaries, and the average annual mortality rate was 21.5%. The mortality rate for west Texas peccaries was calculated at 27.5%. Animal condition, estimated from kidney fat and carcass weight, was highest in the late fall, and was significantly better in the year of high rainfall and good range conditions than during the drought year. Condition of the south Texas peccaries under good range conditions was almost as high as that of pen-reared animals, and under drought conditions almost as low as the west Texas peccaries under good conditions. Males mature sexually at just under a year. Although there are seasonal changes in the proportion of testis constituents, abundant sperm are present in at least some males at all times of the year. Females appear sexually mature at just under a year, but in the wild populations do not become pregnant until 16 to 20 months. Pen-raised animals have a fertile post-partum and lactation oestruses,; and generally, produce two lifters a year. In south Texas 33% of the adult sows showed ovarian evidence of consecutive pregnancies. During favourable range conditions 71% of the collected sows were pregnant and 41% had remated. During drought conditions only 2670 of the sows were pregnant and 9% remated. A good measure of consecutive pregnancies in, west Texas was not obtained, but it appears comparable to south Texas under drought conditions. There was no apparent decrease in reproduction in 15-year old south Texas and 9-year old west Texas females. There was a major breeding period in mid-winter and a minor one in late spring in south Texas. Evidence is limited for west Texas, but most conceptions occur in late winter. Good range conditions arising from favourable rainfall, patterns result in early winter breeding and strong spring breeding activity in south Texas. Drought conditions retard the winter breeding season and almost eliminate late spring breeding. Gross productivity of penned animals was 425 young/100 adult sows. South Texas sows averaged 240 young/100 adult sows during the study. No measure is available for west Texas sows. During good range conditions gross productivity was 288 young/100 adult sows, and during the drought 151 young/100 adult sows. Net productivity in south Texas during the study was 81 under-1-year olds/100 adult sows and 53 (yearlings)/l00 adult sows. In west Texas there were 45 (yearlings)/l00 adult sows. Predation and parasitism are probably of minor importance to the populations. Combined cold weather and drought resulted in a decrease of 29% of two herds, and could function as a factor controlling populations. Draught, through its effect on food availability, appears to be the primary controlling factor of peccary populations in Texas.

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