Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Zimbabwe → Reproductive performance of indigenous and crossbred dairy cattle in the semi arid area of Zimbabwe and the effect of feed supplementation

University of Zimbabwe (2001)

Reproductive performance of indigenous and crossbred dairy cattle in the semi arid area of Zimbabwe and the effect of feed supplementation

Garwe, Evelyn Chiyevo

Titre : Reproductive performance of crossbred cattle developed for milk production in the semi arid tropics and the effect of feed supplementation

Auteur : Garwe, Evelyn Chiyevo

Université de soutenance : University of Zimbabwe

Grade : Doctor of Philosophy (PhD) 2001

Résumé
Three on-station experim ents, one survey and two on-farm studies were undertaken in Matebeleland South Province , Zimbabwe. The objective of these series of studies was to assess the e ffect of feed supplementation and breed on reproductive performance and m ilk yield in cows bred for use in the smallholder dairy sector. In the first on-station experiment, fres hly calved Tuli x Jersey and Nkone x Jersey (crossbred) and Tuli and Nkone (indigenous) cows were offered two diets starting at five days post calving. The diets were ; grazing of natural pasture at a stocking rate of 1LU : 15ha alone or supplemented with 2kg/cow/d of a maize/soyabean-based commercial dai ry meal. Ovarian activity was monitored using milk progesterone pr ofiles. The estimated cumulative probability of ovulation occurring by 200d postpartum for supplemented cows was 0.9 and higher ( P < 0.5) than the probabilit y of 0.63 obtained for unsupplemented cows. Supplement ary feeding also reduced ( P < 0.5) the mean intervals from calving to ovulat ion in indigenous and crossbred cows. There was an interaction ( P < 0.05) between breed and diet on the oestrus detection rates. Indigenous supplement ed cows had the highest increase in oestrus detection rate. The pregnancy and calving rates were higher ( P < 0.05) in crossbred cows than in indigenous co ws. The interaction between breed and diet on pregnancy and calving rates was significant ( P < 0.05). Supplemented indigenous cows had the highest assumed pregnancy rate and supplemented crossbred cows had the highest actual pregnancy rate and calving rate. In indigenous cows, the pregnancy loss rate was increased ( P < 0.05) by supplementary feeding. However, s upplementary feeding reduced pregnancy loss rate ( P < 0.05) in crossbred cows. A ll the supplemented indigenous cows that lost pregnancies were in their firs t parity and all crossb reds that lost pregnancies were multiparous and were not supplemented. The mean daily milk yield was significantly higher in crossbred than in indigenous cows ( P < 0.05). Supplemented cows in both breeds had higher ( P < 0.05) bodyweights than control cows. There was an interaction ( P < 0.05) between breed and diet on body condition scores. Supplement ed indigenous cows had the highest body condition scores. The experimental treatments and met hodology in the second on-station experiment were similar to Experim ent 1 except for milking management. Crossbred cows were superior to indi genous cows in terms of reproductive performance and milk yield ( P < 0.5). The interval from calving to first ovulation was 76 ± 41 d for crossbred and 106 ± 38 d for indigenous cows. Supplementary feeding reduced ( P < 0.05) the interval from calving to first ovulation in both breeds. There was an interaction ( P < 0.05) between breed and diet on the oestrus detection rates. Supplemented indigenous cows had the highest increase in oestrus detection rate. Indigenous cows had higher ( P < 0.05) bodyweights and body condition scores than crossbreds irrespective of diet. There was an interaction ( P < 0.05) between breed and diets on ( P < 0.05) iii bodyweights. Supplemented crossbred cows had the highest increase in bodyweights. In the third on-station experiment, cows were supplemented prepartum using Sorghum bicolor-Lablab purpureus mixed silage. The cows were offered a control diet consisting of grazing natural pasture at a stocking rate of 1LU:15ha and three supplementary diets supplying 0.16, 0.32 and 2 times maintenance (M) energy requirements. Ovarian acti vity was monitored using milk progesterone profiles. Supplem entation at the level of 0.32 M and 2 M improved body condition at calving and reduced the interval from calving to first ovulation in the indigenous cows ( P < 0.05). Interaction between breed and supplementation level on the interval from calving to ovulation was significant ( P < 0.05). Crossbred cows had higher pregnancy rates than indigenous cows across all supplementary feeding levels. The crossbred cows produced higher ( P < 0.001) mean daily milk yields than indigenous cows A survey to assess the reproductive per formance and milk yield of cows in smallholder farming areas was conducted in Gulathi and Irisvale. The farmers claimed that calving intervals were two to three years long and milk yields were 1.5 kg/cow/day. However, there was no information on calving to ovulation intervals, calving rates and lactati on lengths. Based on these findings, an observational study was conducted to m easure the reproductive performance and milk yield of the cows. Milk yiel d, bodyweight and body condition scores were measured starting from calving. Milk progesterone was used to assess reproductive performance. The study s howed that out of 36 cows monitored only three crossbred cows had ovul ated by 200 days postpartum. A mean interval from calving to ovulation of 63 ± 29 d and a calving rate of 3% were obtained. Average daily milk yield was 1. 2 ± 0.9 kg and lact ation length was 174 ± 47 d. A second on-farm study was carried out to determine the effect of feed supplementation on reproductive perform ance and milk yield. Cows on the control diet were allowed to graze on natural pasture at a stocking rate of 1LU:20ha. In addition to graz ing of natural pastures, supplemented cows were offered 2kg/cow/day of a maize/so yabean-based dairy meal starting from calving until conception. S upplementary feeding reduced ( P < 0.05) the interval from calving to ovulation from 132 ± 63 d to 102 ± 69 d. Oestrus detection rate was increased ( P < 0.05) by supplementary feeding from 10% to 41%. Supplementary feeding increas ed conception rate from 35% to 80% and calving rate from 18% to 65% over two seasons. Daily milk yield increased from 1.26 ± 0.5 kg to 3.3 ± 1.3 kg. The studies demonstrated that feed supplementati on was beneficial in improving reproductive performance and m ilk yield of cows in smallholder farming sectors. In addition, crossbred cows were superior to indigenous cows in terms of their reproductive performance and milk yield.

Mots clés : Dairy cattle // reproduction // indigeneous // crossbreed // semi-arid area // feed supplement // Zimbabwe

Version intégrale

Page publiée le 24 mars 2015, mise à jour le 16 juin 2017