Animal welfare and effects of per-female stress on male and cattle reproduction-A review

Abstract

Thermal stress causes severe effects on the wellbeing and reproduction of cattle, including changes in oogenesis and spermatogenesis, generating great concerns, which last for decades. In cattle, the occurrence of thermal stress is associated with a reduction in the production of spermatozoids and ovarian follicles, in addition to the increase of major and minor defects in gametes or in their intermediate stages. In bovine females able to reproduce, a reduction in the rate of estrus manifestation and an increase in embryonic mortality has been observed. Therefore, keeping animals on good welfare conditions, with water supply and in shaded areas can favor the improvement of different reproductive parameters. For all this, the present study aimed to gather, synthesize and argue recent studies related to animal welfare, focusing on the effects of thermal stress on the reproduction of cattle, aiming to support possible strategies to mitigate the harmful effects of thermal stress in this species.

Keywords: heat load; reproduction; spermatogenesis; thermal stress; thermotolerance.

Figure 1

Critical temperatures and thermo-neutral zone in dairy cattle. Adapted from Avendaño-Reyes (15).

Figure 2

Temperature-humidity index (THI) table for dairy producer to estimate heat stress for dairy cows. Deg, Degrees. Relative humidity expressed as percentage. Adapted from Armstrong (23).

Figure 3

For milk production, the yield was relatively constant up to about 24°C and then began to decline as the temperature increased. Adapted from the study developed by Ravagnolo et al. (35).

Figure 4

Impact of heat stress on female reproductive performance. Adapted from Krishnan et al. (37). Mitigation of the heat stress impact in livestock reproduction.

Figure 5

Impact of heat stress on pregnancy in livestock. Adapted from Krishnan et al. (37). Mitigation of the heat stress impact in livestock reproduction.

Figure 6

Aspects of the main impacts caused by heat stress during cattle handling. Adapted from Krishnan et al. (37).

Figure 7

Schematic drawing on the main aspects that affect cattle, as well as the mediators of stress in the animal, and finally the associated strain that affects the pregnancy outcome. HPG, hypothalamic-pituitary-gonadal; HPA, hypothalamic-pituitary-adrenal. Adapted from Matthew (52).

Figure 8

Illustration of the initial response when there is a stressor stimulus in cattle. The sympathetic nervous system stimulates the adrenal gland to release catecholamines [adrenaline (AD) and noradrenaline (NAD)] and cortisol (CT).

Figure 9

Infographic of environmental effects on physiological, behavioral and stress parameters in male and female cattle conditioned in sun and shade systems. Adapted from Edwards-Callaway et al. (82). TA, Ambient Temperature.

Figure 10

Effects of heat stress on bovine embryo development and heat shock protein (HSP) production (42).

Figure 11

Bovine testis. (A) Morphological characteristics of the testis without heat stress. (B) Morphological characteristics of the testis under heat stress.

Figure 12

Illustration of the effects of heat stress on male bovine reproduction. ACTH, adrenocorticotropic hormone, or corticotropin; CRH, corticotropin releasing hormone. Adapted from Krishnan et al. (37) and Singh et al. (172).