Understanding the trade-off between the environment and fertility in cows and ewes

Abstract

The environment contributes to production diseases that in turn badly affect cow performance, fertility and culling. Oestrus intensity is lower in lame cows, and in all cows 26% potential oestrus events are not expressed (to avoid getting pregnant). To understand these trade-offs, we need to know how animals react to their environment and how the environment influences hypothalamus-pituitary-adrenal axis (HPA) interactions with the hypothalamus-pituitary-ovarian axis (HPO). Neurotransmitters control secretion of GnRH into hypophyseal portal blood. GnRH/LH pulse amplitude and frequency drive oestradiol production, culminating in oestrus behaviour and a precisely-timed GnRH/LH surge, all of which are disrupted by poor environments. Responses to peripheral neuronal agents give clues about mechanisms, but do these drugs alter perception of stimuli, or suppress consequent responses? In vitro studies confirm some neuronal interactions between the HPA and HPO; and immuno-histochemistry clarifies the location and sequence of inter-neurone activity within the brain. In both species, exogenous corticoids, ACTH and/or CRH act at the pituitary (reduce LH release by GnRH), and hypothalamus (lower GnRH pulse frequency and delay surge release). This requires inter-neurones as GnRH cells do not have receptors for HPA compounds. There are two (simultaneous, therefore fail-safe?) pathways for CRH suppression of GnRH release via CRH-Receptors: one being the regulation of kisspeptin/dynorphin and other cell types in the hypothalamus, and the other being the direct contact between CRH and GnRH cell terminals in the median eminence. When we domesticate animals, we must provide the best possible environment otherwise animals trade-off with lower production, less intense oestrus behaviour, and impaired fertility. Avoiding lifetime peri-parturient problems by managing persistent lactations in cows may be a worthy trade-off on both welfare and economic terms-better than the camouflage use of drugs/hormones/feed additives/intricate technologies? In the long term, getting animals and environment in a more harmonious balance is the ultimate strategy.

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“…However, moderately lame, lame and severely lame cows had about 190 to 500 days open or CCI, hence, the number of days from calving to conception was doubled for ). In addition, lameness has been reported as the secondplaced production disease responsible for increasing days open after caesarean, and it is rated above other diseases such as endometritis, placental retention, dystocia, mastitis and milk fever (Dobson et al, 2020;Walker et al, 2008). Although our results are similar to those described above, the higher increase of days open due to lameness stands out in this herd; which is probably due to the high proportion of clinically lame cows that mainly corresponded to evidently lame cows.…”

Estrus expression and pregnancy rates in heifers primiparous and multiparous Nelore cows subjected to timed artificial insemination with strategic use of gonadotropin-releasing hormone

“…Animals with a negative energy balance do not have sufficient luteinizing hormone (LH) peaks to promote ovulation (Cheong et al, 2016;Meteer, Shike, & Cardoso, 2015). Another factor that can impair ovulation in lactating cows is the sensory interaction between the cow and the calf; according to Dobson, Routly and Smith (2020), this interaction stimulates the secretion of endogenous opioids by the hypothalamus, thereby inhibiting GnRH secretion and consequently the frequency of LH peaks necessary for ovulation. In addition, the suckling calf has a suction effect, which has been related to the reduction in the amount of intrafollicular receptors for LH (Barreiros et al, 2014;Campos, Marinho, Lunardelli, Morotti, & Seneda, 2013;Dobson et al, 2020).…”

Association between luteinizing hormone level decrease on the triggering day and pregnancy outcome for in vitro fertilization/intracytoplasmic sperm injection patients following gonadotropin-releasing hormone antagonist protocol: a retrospective cohort study

“…Kallmann syndrome is a common congenital deficiency in GnRH secretion that can lead to low LH levels. Psychogenic stress, weight loss, anorexia nervosa, chronic strenuous exercise, Sheehan syndrome, empty sella syndrome, and drugs that inhibit GnRH secretion in the hypothalamus can also lead to low LH levels [21][22][23][24] . COH during ART involves using drugs (GnRH-as or GnRH-As) to regulate the secretion of GnRH by the hypothalamus and the secretion of LH and FSH by the pituitary.…”