Pregnancy, Parturition and Resumption of Ovarian Cyclicity in Beef Cows

Research Article

Austin J Vet Sci & Anim Husb. 2022; 9(4): 1100.

Pregnancy, Parturition and Resumption of Ovarian Cyclicity in Beef Cows

Bruce T¹ and Soul W²*

¹Department of Research and Specialist Services, Matopos Research Institute, Zimbabwe

²Department of Livestock, Wildlife & Fisheries, Great Zimbabwe University, Zimbabwe

*Corresponding author: Washaya Soul, Department of Livestock, Wildlife & Fisheries, Great Zimbabwe University P.O Box 1235 Masvingo, Zimbabwe

Received: August 01, 2022; Accepted: August 29, 2022; Published: September 05, 2022


Communal farmers find it very difficult to control animal breeding hence fixed Time Artificial Insemination (TAI) is a promising technique. The objective of this study was to determine the effects of bull age and breed on pregnancy rate, and the post-partum interval in extensively managed communal beef cows. A total of 577 female animals with a body condition score between 2.5 and 3, from three breeds; Brahman (189), Nkone (18) and Mashona (370) were used. Fixed time artificial insemination using the ovsynch protocol was done using semen from four different bull breeds (Mashona, Tuli, Brahman and Boran) aged between 3 to 6 years. The percentage of cows identified pregnant were analysed using generalized linear mixed model PROC GLIMIXX of SAS. The effects of cow parity on PPI were evaluated using the general linear model of SAS. Conception rates were 53.2; 57.3 and 75% for Brahman, Mashona and Nguni cows respectively. Animals in their third parity had the highest conception rate. Young bulls less than 3 years of age had the least pregnancy rate while Mashona bulls had the highest pregnancy rate. There was a breed by parity interaction on PPA interval (P < 0.05). It can be concluded that PGF2α and Estradiol Benzoate (EB) could be successfully used to induce and synchronize ovulation in cattle undergoing TAI, sire age significantly influenced conception rate as well as that the post-partum interval is dependent on breed and parity.

Keywords: Conception; Indigenous breeds; Postpartum anoestrus; Small scale beef production


Beef cattle serve a unique role in converting low quality forage to high-quality protein for human consumption [17]. In most smallholder beef enterprises, cowherds are characterised by uncontrolled breeding, low plane of nutrition and rampant calving. In sub-Saharan Africa performance of this sector is affected by various factors including breed, geographical location, season of calving, suckling status, age, parity, and body condition score [55]. In such production systems profitability is rarely talked about , however farmers realise that it hinges on producing as many calves as possible per cow per lifetime [47]. Furthermore, the businesses is predominantly part-time where small herds of animals are frequently run on fragmented land with limited access to handling facilities. Under such conditions productivity is a term not applicable, not to mention the use of advanced technologies like AI. Nonetheless the demand for beef is increasing and technologies that can improve the quantity and quality of beef are germane.

In this regard herd fertility becomes critical, and it has been promoted that fertility of the herd, among other factors, underpins the profitability of a beef enterprise [36]. At least in the cow, fertility is measured by conception rate/pregnancy rate, and calving rate. The use of oestrous synchronisation has been promoted as probably the only applicable reproductive biotechnology to facilitate AI in beef cattle [1,6]. Unfortunately, due to the extensive nature of the productive system, it is no secret that, AI has strong barriers to implementation at farm level.

In this study, pregnancy rate and Post-Partum Anoestrus (PPA) were used as a measure of fertility. In order to achieve a calf every year, cows should conceive between 75 to 85 days following parturition. More often than not, smallholder beef animals exceed this period. The reasons could be related to nutritional inadequacies [17,55] that leads to low LH pulse frequency [17], seasonal variations [2], suckling and maternal bond inhibiting ovulation [17]. It has been observed that beef cows exhibit early resumption of follicular growth within 7 to 10 days postpartum [47], however the time to ovulation is limited to more than 80 days probably due to lack of ovulation stimulus and not lack of follicle growth. Resumption of ovulation and oestrous cycles are key requirements to facilitate rebreeding of postpartum cows. It has been reported that beef cows have a prolonged interval to resumption of ovulation compared to dairy [17] and this is because of suckling and maternal bond-inhibiting ovulation. [18] Reported that following an uncomplicated calving, approximately 30 days are required for completion of uterine involution in beef cows. In addition resumption of normal ovarian cyclicity and oestrus depends on the recovery of the hypothalamic–anterior pituitary– ovarian axis, in particular the attainment of a GnRH/LH pulse frequency of 4 to 5 pulses per 10 h period. This can only happen in commercialised entities with expect gadgets to monitor these hormonal levels and is generally not practical in smallholder farming systems.

Furthermore, beef cows in good Body Condition (BC) have been shown to have a mean of 3.2 ± 0.2 dominant follicles (~30 days) to first ovulation [2,17]. If these animals are in poor BC the number of follicles drops and period to first ovulation increase to ~70 to 100 days [2]. The lack of ovulation and dominant follicles during this period has been associated with infrequent LH pulses, suckling, maternal– offspring bonding and low Body Condition Score (BCS) [17]. The key to optimizing the resumption of ovulation in beef cows relates to appropriate pre-calving nutrition and management, this ensures that cows calve down in optimal body condition ranging between 2.75 to 3.0 [2,47]. Conception and subsequent pregnancy rate in beef cows following the initiation of postpartum ovarian cyclicity solely is a function of bull fertility in small holder naturally serviced herds [18]. To this end bull age and breed are critical in the evaluation of beef cows’ fertility status. As reported by [26,47-49,52,55], bull age and breed significantly affect pregnancy rates in beef cattle production. Therefore the objective of this study was to determine the effects of bull age and breed on pregnancy rate, and the post-partum interval in extensively managed communal beef cows.

Materials and Methods

Study Site

The study was carried out in Mwenezi District which is located in Agro-ecological Region V (21° 25’ 0”S, 30° 44’ 0” E) on the South East Lowveld of Zimbabwe. Mwenezi District lies at an altitude of 558masl. The district is drought prone, characterized by low and erratic rainfall of about 400mm/ year [29] recording maximum temperatures of 34°C in October and an average minimum temperature of 5°C occurring in July [15]. This area falls in a transition zone between broken granite country to the north and the flat, fertile mixed bushlands of the south east lowveld. There are many domed hills and castle kopjes interspersed with gently sloping areas and thickly wooded river valleys. Acacia, Combretum and Mopane trees provide livestock food, together with perennial forbes and shrubs which supply nutritious green shoots [29]. Sand veld sites are characterised by species low in digestible crude protein, while clay veld areas are typified by high quality fodder grasses. Grasses include Themedatriandra, Eraqrostis spp, Cenchrusciliaris. Urochloa spp, and some Panicum maximum, and these are mostly palatable and of high value as grazing. Heteropogoncontortus, Themedatriandra, Eraqrostissuperba and Diqitaria spp), and where soils are deep a good sward of Panicum maximum and Urochloapullulans and other good grazing grasses can be found. (Figure 1) shows the study area.

Study Animals and Selection Criteria

A total of 567 female animals from three breeds; Brahman (189), Nkone (8) and Mashona (370) were selected. Heifers and cows from first to sixth parity with a body condition score ranging from 2.5 to 4 were selected. These animals were derived from 8 wards in which farmers on a willing basis were required to provide them with feed and drink. A central insemination holding paddock in each ward was erected, which lasted for two weeks, with the help of Agritex and Veterinary officers. Two paravets from each ward among the local farmers were identified and trained with the help of Agritex and Veterinary officers. They were responsible for mobilizing farmers to join the program, general health of the cows. Insemination was done by two trained technicians from Matopos Research Institute.

Cow Breeding

Fixed time artificial insemination using the ovsynch protocol that uses Estradiol benzoate (estrogens), Prostaglandins F2α (PGF2α) analogue and Controlled Internal Drug Release (CIDR), was doneusing semen from four different breeds (Mashona, Tuli, Brahman and Boran) aged between 3 to 6 years, with an unbalanced semen breed allocation design following farmer preferences. A shot of Estradiol Benzoate was administered to the animals at 2ml/ animal intramuscular on day 0 and a CIDR loop inserted. The inserted CIDR was in form of an intravaginal insert containing 1.9g of progesterone. On Day 7 the CIDR loop was removed and the animals received a PGF2α (Estrumate) injection at 2ml/animal and the animals confined. A second shot of Estradiol Benzoate was administered intramuscular on Day 8 at 1ml/animal. Timed artificial insemination was performed on Day 10. Farmers provided feed and water to their animals during the confinement period as this was one of the preselection requirements. Animals were let go on Day 11.

Data Collection

Insemination records that included insemination date, semen breed and age, dam predominant breed, post calving period (months), and parity were recorded. Pregnancy diagnosis through rectal palpation was done 90 days following the fixed time artificial insemination with the pregnancy statuses being recorded.

Confirmation of Pregnancy

To confirm pregnancy all animals were subjected to pregnancy diagnosis after 90 days post breeding as described by Arthur [3]. Conception Rates (CR) were estimated from the proportion of pregnancies confirmed by rectal palpation among the total number of cows and heifers bred using the formulae prescribed by Banerjee [5].