Applying assisted reproductive technology and reproductive management to reduce CO2-equivalent emission in dairy and beef cattle: a review

Methane emission from beef and dairy cattle combined contributes around 4.5-5.0% of total anthropogenic global methane. In addition to enteric methane (CH4) produced by the rumen, cattle production also contributes carbon dioxide (CO2) (feed), nitrous oxide (N2O) (feed production, manure) and other CH4 (manure) to the total greenhouse gas (GHG) budget of beef and dairy production systems. The relative contribution in standard dairy systems is typically enteric CH4 58%, feed 29% and manure 10%. Herds with low production efficiency can have an enteric CH4 contribution up to 90%. Digestibility of feed can impact CH4 emission intensity. Low fertility herds also have a greater enteric CH4 contribution. Animals with good feed conversion efficiency have a lower emission intensity of CH4/kg of meat or milk. Feed efficient heifers tend to be lean and have delayed puberty. Fertility is a major driver of profit in both beef and dairy cattle, and it is highly important to apply multi-trait selection when shifting herds towards improved efficiency and reduced CH4. Single nucleotide polymorphisms (SNPs) have been identified for feed efficiency in cattle and are used in genomic selection. SNPs can be utilized in artificial insemination and embryo transfer to increase the proportion of cattle that have the attributes of efficiency, fertility and reduced enteric CH4. Prepubertal heifers genomically selected for favourable traits can have oocytes recovered to produce IVF embryos. Reproductive technology is predicted to be increasingly adopted to reduce generation interval and accelerate the rate of genetic gain for efficiency, fertility and low CH4 in cattle. The relatively high contribution of cattle to anthropogenic global methane has focussed attention on strategies to reduce enteric CH4 without compromising efficiency and fertility. Assisted reproductive technology has an important role in achieving the goal of multiplying and distributing cattle that have good efficiency, fertility and low CH4.(AU)

Produção e metabolismo da progesterona e seu papel antes, durante e depois da inseminação artificial influenciando a fertilidade de vacas leiteiras de alta produção / Progesterone Production and Metabolism and Its Role Before, during and after Artificial Insemination Influencing the Fertility of High Producing Dairy Cows

Background: Efficient reproduction performance is important for optimal profitability on dairy operations. Unfortunately, most dairy farms do not attain optimal reproduction due to many factors including management, health, and physiology of high-producing dairy cows. The physiology limitations involved in reproduction of lactating dairy cows are complex and becoming worse as milk production increases. But many variables related to the interactions between nutrition, the complexity of some hormonal systems, and altered reproductive patterns in dairy cattle have been elucidated. This review will focus on the role of progesterone (P4) in reproduction of the lactating dairy cow. Review: Progesterone is a steroid hormone primarily secreted by the corpus luteum (CL) and placenta. Adequate circulating P4 concentrations are essential for establishment and maintenance of pregnancy. Thus, because of the central role of progesterone on fertility, this manuscript reviews the effect of progesterone (P4) during timed AI protocols in lactating dairy cows. Two sections summarize how P4 is produced and a model attempts to explain how P4 is metabolized in high producing dairy cows. Circulating P4 is determined by a balance between P4 production and P4 metabolism and stimulatory and inhibitory pathways regulating this balance are complex. However in dairy cattle, the volume of luteal tissue is a primary factor regulating P4 production; although, inadequate P4 is generally due to high metabolism of P4 resulting from extremely elevated liver blood flow. If P4 production is increased by an increase in luteal tissue without a change in liver blood flow, then circulating P4 will increase. Conversely, if there is an increase in liver blood fl ow then there will be a corresponding decrease in circulating P4 even though P4 production has not been altered. Thus, an understanding of regulation of circulating P4 must carefully consider the factors regulating P4 production and its metabolism. As will be discussed below, over 80% of P4 production during the estrous cycle of the cow is due to constitutive P4 production by the large luteal cell. Regulation of constitutive P4 production by the CL does not appear to require stimulatory pathways but can be dramatically decreased during luteolysis induced by exogenous or endogenous prostaglandin F2α (PGF2α). Conversely, although liver enzymes involved in P4 metabolism can be regulated, we speculate in this model that the primary determinant of P4 metabolism in the lactating cow is related to the rate of liver blood flow. These concepts are more fully discussed below. Three sections summarize the role of P4 concentrations prior to breeding, near the time of breeding, and after breeding. During timed AI protocols, elevations in P4 are achieved by increasing number of CL by ovulation of accessory CL or by supplementation with exogenous P4. Elevating P4 prior to the timed AI generally decreases double ovulation and can increase fertility to the timed AI. Near the time of AI, slight elevations in circulating P4 can dramatically reduce fertility with inadequate luteolysis to the PGF2α treatment prior to timed AI, being the underlying cause of this problem. After AI, circulating P4 is critical for embryo growth and establishment and maintenance of pregnancy. Many studies have attempted to improve fertility by elevating P4 after timed AI with primarily marginal elevations (<5%). Conclusion: Previous research has provided substantial insight into mechanisms regulating circulating P4 concentrations and actions. Understanding this prior research can focus future studies on P4 manipulation to improve timed AI protocols.