Environmental constrains on post-partum ovarian activity in Tanzanian Zebu cows.

Milk progesterone measurements were used to study post-partum ovarian activity and risk factors for ovarian dysfunction in Zebu cows reared under a traditional pastoral management system in three villages in Morogoro region, Tanzania. Milk samples for progesterone analysis were collected twice per week from a total of 98 lactations. The most prevalent ovarian dysfunction detected was delayed onset of post-partum ovarian activity and cessation of cyclical ovarian activity after a period of normal ovarian function. Prolonged luteal phases were not observed. Resumption of post-partum ovarian activity was observed in 61 (62.2%) cows. Pregnancy was diagnosed in 43 (43.8%) out of 98 cows and was terminated by abortion in 7 (16.3%) cows. The median number of days from calving to resumption of ovarian activity was lower in cows that calved during the dry season (167 days) as compared with those that calved in the rainy season (200 days, P=0.03), probably because ovarian function was stimulated in cows entering the rainy season first after the puerperal phase had ended. Cyclical ovarian activity ceased in seven (11.5%) cows, and all but one case of cessation of ovarian activity took place during the dry season. Cows in their first and second parities experienced prolonged intervals (244 days) between calving and onset of ovarian activity compared with cows in their third or later parity (172 days, P=0.03). Cows with marked losses in body condition experienced prolonged intervals between calving and onset of ovarian activity (229 days) as compared with cows that lost <1 body condition unit (172 days, P=0.03). The time interval from calving to resumption of ovarian activity varied between the three villages of the study (142, 192 and 229 days, P=0.05), indicating local differences in management practices.

A study on reproductive performance and related factors of zebu cows in pastoral herds in a semi-arid area of Tanzania.

A prospective longitudinal study was carried out from September 2001 to June 2004 in three adjacent villages in a semi-arid area of Tanzania. The objectives of this study were to measure the intervals between calving and either resumption of cyclical activity or confirmation of pregnancy, to estimate calving intervals, and to investigate the effect of factors assumed to be related to postpartum reproductive performance. A total of 275 lactation periods from 177 Tanzanian Shorthorn Zebu cows managed in a traditional pastoral system in 46 households were initially included. Animals were initially screened for brucelosis and thereafter examined by palpation per rectum at 2-week intervals. Body condition score (scale 1 to 5) was assessed and girth measurement (cm) taken. Occurrence of other reproductive events such as calving, abortion, death of calf, culling and reason for culling were recorded. In a subset of 98 lactation periods from 91 cows milk samples for progesterone (P4) determination were collected twice per week from day 7 after calving to the time of confirmed pregnancy or until milk production ceased before pregnancy. The data were analysed both univariately and in multivariable Cox proportional hazard (frailty) models. The mean (+/-S.E.M.) calving interval was 500+/-13.6 days. Positive reactors in the brucellosis test were 15.6% of the tested animals. Milk P4 analysis showed the rate of abortion/late embryo loss to be 14.3%. Calf mortality rates varied between 14.6 and 17.4%. A positive relationship was found between the outcome variables likelihood of cyclical activity and likelihood of pregnancy in the Cox model, and the explanatory variables: parity and body condition score (BCS) at calving. A negative relationship was found between the outcome variables, and the explanatory variables: maximum BCS loss and calf survival/mortality. Calving in the rainy season was associated with an increased likelihood of pregnancy.

Seasonal changes in nutritional status and reproductive performance of Zebu cows kept under a traditional agro-pastoral system in Tanzania.

The objectives of this study were to assess changes in nutritional status/body condition score, percentage pregnancy and calving rate in Zebu cows and to establish the relationship between body condition score loss and postpartum interval to resumption of ovarian activity. A total of 198 cows and postpubertal heifers of the Tanzanian Shorthorn Zebu kept under a traditional management system were randomly selected from 200 smallholder herds. Factors investigated during bi-weekly visits include body condition score (BCS), heart-girth circumference, milk yield and reproductive status of the animals, pregnancy/nonpregnancy and cyclicity/non-cyclicity. Local weather conditions and dates of occurrence of other reproductive events such as calving were also recorded. Calvings occurred all year round but with a strong seasonal distribution characterized by annual peaks observed between April and July. The annual calving pattern was closely related to rainfall, with peak precipitation occurring a few months before peak calving. The overall percentage pregnancy varied from 30% to 50% throughout the year. Postpartum cows exhibited minimum mean BCS and heart-girth circumference 12-14 weeks after calving, and cows with BCS loss >1 point exhibited the longest time interval from calving to onset of ovarian activity.

Effect of parity, season and FSH treatment on the calving interval of Ayrshire cows in the tropics.

A total of 607 calving intervals on 99 Ayrshire cows with parities from 1 to 10 and belonging to one dairy herd at Iringa in the southern highlands of Tanzania were analysed to study the effect of parity and season or month of calving on the subsequent calving interval. In addition, 22 calving intervals incorporating a superovulatory cycle were compared with those of 52 controls that had calved around the same period. The average (mean +/- SEM) age at first calving was 985 +/- 16 days. The effect of parity on calving interval was highly significant (p < 0.001). Cows that calved in December, at the beginning of the rainy season, exhibited the shortest calving interval (404 +/- 13), while those that calved in September/October, in the dry season, exhibited the longest average calving interval (466 +/- 20 days), although this difference was not significant. Prior treatment with follicle-stimulating hormone to induce superovulation, significantly lengthened the average calving interval (579 +/- 28 vs 457 +/- 15 days; p < 0.001). It was concluded that both parity and FSH treatment affected the calving interval. However, season (rainy vs dry) or month of calving did not influence this interval.

Suboptimal reproductive performance of dairy cattle kept in smallholder herds in a rural highland area of northern Tanzania.

The objectives of the present study were to assess the reproductive performance and cumulative incidence risk of reproductive disorders and to compare the success of artificial insemination (AI) to natural service (by handmating; NS) in dairy cattle kept in smallholder herds under a zero-grazing system in a rural highland area of Tanzania. Data on occurrence of all normal and abnormal reproductive events were collected for 215 adult animals belonging to 74 households. The median and range of the intervals: intercalving, calving to first service, and calving to pregnancy were 477 (335-860), 154 (38-486) and 206 (61-567) days, respectively. Breed and parity did not affect the reproductive parameters (P>0.05). However, cows in the milked group had a shorter median calving interval than those in the suckled group (P<0.001). The overall percentage pregnant and the percentage pregnant to first service were higher in the NS than in the AI group (49 vs. 32%; P=0.007) and (67 vs. 25%; P<0.001), respectively. The median numbers of services per pregnancy were not different between the AI (3) and NS (2) groups (P=0.17). The cumulative incidence risk of abortion, dystocia, prolapse, retained fetal membranes, mastitis, milk fever and cyclic non-breeders were 16.0, 1.7, 2.5, 4.2, 5.0, 1.7, and 6.1%, respectively. Hoof overgrowth (4.6%) and hoof deviation (4.6%) were the most-frequent digital problems. We concluded that reproductive parameters and cumulative incidence risk of abortion show suboptimal reproductive performance in rural-based, zero-grazed smallholder dairy herds in Tanzania particularly those using AI.