Biomedical subjects

J M Dzakuma

Publications and source records attributed to J M Dzakuma.

4 recordsLinked to original sources

PubMed1989

Computer modeling of sheep reproduction: I. An algorithm for quantifying anestrous cycles in ewes.

An algorithm that mathematically describes annual estrous activity in ewes is given. The function fitted as the ordinate is similar to a normal distribution function related to date as the abscissa. The data used were collected from literature on different breeds and from different locations of the world; all studies had been specifically conducted to study estrous activity in ewes in these locations. Parameters estimated in an iterative procedure from the algorithm were length of time during which estrous cycles occurred (SA), a measure of asymmetry (SD), day of mid-estrous (DE), highest incidence of estrus (MX) and lowest incidence of estrus (MN), day of lowest incidence of estrus (DN) and day of mid-anestrous season (DA). Incidence of estrus is defined as the proportion of ewes exhibiting an active estrus. These parameters were estimated for several breeds and locations. The data, as collected, were inadequately cross-classified to allow for unconfounded estimation. However, analyses of fitted parameters that describe the curves gave quantitative results about the influences of breed of sheep, location, latitude and altitude and indicated which parameters were associated with these factors. Breeds differed significantly for SA, DE, MX and DA. Locations differed for DE, MX and DA. Latitude was associated with differences in DE, DN and DA with altitude also associated with differences in DE and DA. There were no significant effects on SD even though breeds differed sizably in SD.

Algorithms↗

PubMed1989

Computer modeling of sheep reproduction: II. Accelerated reproduction in sheep.

A computer simulation program was written in SLAM (Simulation Language for Alternative Modeling) to simulate certain biological aspects involved in alternative systems of reproduction in sheep. Four fundamental lambing schemes, once a year, three times in 2 yr, twice a year and continuous schemes, along with modifications of these schemes, are simulated. Parameters of greatest effect in this simulation were the average spread of the estrous season (SA), the measure of asymmetry (SD) and the maximum proportion of ewes exhibiting estrus (MX). It was demonstrated that the greater the SA values (longer estrous seasons and shorter anestrous seasons), the more advantageous it was to breed frequently. The SD and MX parameters influenced to a lesser degree the lambing results obtained from these simulations. The relative merits of certain breeds and locations for out-of-season breeding were studied and evaluated for annual and seasonal fertility.

Algorithms↗

PubMed1982

Fertility and prolificacy of crossbred ewes under two cycles of accelerated lambing.

The reproductive performance of 227 crossbred ewes representing five combinations of Finnsheep (F), Dorset (D) and Rambouillet (R) breeding was evaluated under two cycles of accelerated lambing, with lambing every 8 mo. The five breed combinations represented were: 1/2D 1/2R, 1/4D 3/4R, 1/4F 1/2D 1/4R, 1/4F 1/4D 1/2R and 1/4F 3/4R. The ewes were 4 and 5 yr old when put on the accelerated lambing program. Ewes were mated to yearling Hampshire, Suffolk, HxS or SxH crossbred rams each season. Each cycle was made up of three breeding seasons: winter (January-February), fall (September-October) and late spring (May-June). Reproductive performance averaged over the two cycles showed reduced fertility to May-June breeding (47.8%), compared to January-February breeding (91.8%) and September-October breeding (90.6%; P less than .05). During May-June breeding, 1/2D 1/2R ewes were more fertile (P less than .05) than 1/4D 3/4R or any 1/4F ewe groups. During the winter and fall breeding seasons, ewe fertility averaged 91.5% and was similar for ewes exposed to purebred and crossbred rams. In the late spring the use of crossbred rams resulted in 62.4% conception compared with 41.0% from the use of purebred rams (P less than .05). Prolificacy of the ewes averaged 1.67 lambs during winter, 1.80 lambs during fall and 1.35 lambs during later spring. The 1/4F ewe groups produced .10 and .16 more lambs/lambing (P less than .05) than 1/2D 1/2R and 1/4D and 3/4R ewes, respectively.

Animals↗

PubMed1982

Repeatability of lambing rate.

Repeatability of number of lambs born using the life-time records on 263 crossbred ewes produced in 1971 and 1972 were estimated by the intraclass correlation method and by the regression of subsequent lamb production on number of lambs born alive at the first and second lambings. The ewes were of Finnsheep (F), Dorset (D) and Rambouillet (R) breeding and first lambed at 1 yr of age. Five breed combinations were represented 1/2D 1/2R 1/4R 3/4R, 1/4F 1/2D 1/4R, 1/4F 1/4D 1/2R and 1/4F 3/4R. Ewes were bred to yearling Hampshire, Suffolk or reciprocal cross rams at varied intervals in the course of study. The repeatability of number of lambs born estimated by intraclass correlation was .138 +/- .067. Repeatability of number of lambs born estimated by the regression of subsequent lamb production on initial lambing rate was .121 +/- .025 lambs/ewe season and that estimated by the regression of subsequent lamb production on second lambing rate was .046 +/- .020 lambs/ewe season. Ewes producing twins at their first lambing subsequently produced an average of .11 more lambs/lambing than ewes producing singles and ewes producing singles subsequently produced an average of .16 more lambs/lambing than ewes than produced no lambs. Differences between these lambing classes at the second lambing were small (.05 and .06). The first lambing at 1 yr of age was a much better predictor of the ewes' lifetime lambing rate.

Animals↗