BREEDING ▶▶▶
6 management factors to consider in herd fertility
Fertility is a complex trait that is difficult to genetically improve because of low heritability. It can, however, be improved.
BY SALAH H. ESMAIL I
Covering the floors with rub- ber helps in- crease the effi- ciency of oestrogen detection.
mproving fertility through other ways can occur such as; control of climatic conditions, adequate nutrition and proper management practices. The following is a review of these practices which affect fertility and hence affect the financial sustainability of dairy herds.
1. Thermal stress During heat stress, there is a reduction in blood flow to the uter-
us and increased blood flow to the surface. As a result of the de- creased blood flow to the uterus, the uterus becomes ‘hot’ and the embryo will suffer high temperatures. There is also a reduc- tion in the supply of energy substrates such as glucose and VFA’s (volatile fatty acids) to the uterus so that insufficient nutri- tion will be available to the foetus to sustain its development. Cold stress, on the other hand, may not detrimentally affect fertility or foetal condition. If, however, too much reliance is placed on using body energy reserves where the feeding lev- el is insufficient or protein is deficient, complications such as the weak calf syndrome may arise. With sever reduction in body condition, cows may have reduced lactation potential and may experience delays in rebreeding.
The thermal effects can be mitigated through modification of the microclimate of animals. The provision of shades, fans, sprinklers, and cold water in summer and windbreaks with adequate litter materials in winter can be of great help. Other management practices, including nutrition and health care, should also be considered.
2. Nutrition Experiments have shown that the heifers that are adequately
fed show earlier oestrus cycle than the others with poor nutri- tion. The differences between the two groups in the incidence of oestrus cycles were found to be 128 days in the Friesian, 65 days in Jersey, and 100 days in the Ayrshire cows. Other exper- iments showed that the level of nutrition also affects the age of sexual maturity of the females. In these experiments, one group of heifers was fed a poor diet and reached puberty at 710.7 days of age, while another group was fed an adequate diet with proper protein-energy balance and reached puberty at 440.1 days. The level of mineral salts in the diet also affects the fertility of female animals. Phosphorus deficiency, for ex- ample, leads to delayed oestrus due to the low secretion of oestrogen, and may also lead to dystocia which sometimes re- sults in the death of the dam or the foetus. Nutrition has a clear effect on the fertility of male animals as well. A low plane of nutrition suppresses the production of gonadotropins by the pituitary gland and the secondary sex hormones so that atrophy of the prostate and seminal vesi- cles occur thereby affecting semen quality in terms of fluid volume and concentration. Vitamins also play an important role in the fertility of male animals. For example, Vitamin A deficiency lowers the sper- matozoa concentration, semen storage capacity and also de- layed sexual maturity and suppressed spermatogenesis in young bulls.. Vitamin E deficiency, on the other hand, increas- es the number of mountings needed for conception due to a reduced rate of cellular metabolism, degeneration of the ger- minal epithelium and testicular degeneration which, may lead to reduced spermatogenesis with a resulting poor semen output and quality.
3. Photoperiod The increased photoperiod affects the reproductive perfor-
mance of the animal. The mating period and the number of 14 ▶DAIRY GLOBAL | Volume 7, No. 1, 2020
PHOTO: KOOS GROENEWOLD
PHOTO: MISSET
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