Denise Hough

Exploration of the Hypothalamic-Pituitary-Adrenal Axis to Improve Animal Welfare by Means of Genetic Selection: Lessons from the South African Merino

Simple Summary Breeding sheep that are robust and easily managed may be beneficial for both animal welfare and production. Sheep that are more readily able to adapt to stressful situations and a wide variety of environmental conditions are likely to have more resources available for a higher expression of their production potential. This review explores the utilization of one of the stress response pathways, namely the hypothalamic-pituitary-adrenal axis, to locate potential sites where genetic markers might be identified that contribute to sheep robustness. A South African Merino breeding programme is used to demonstrate the potential benefits of this approach. Abstract It is a difficult task to improve animal production by means of genetic selection, if the environment does not allow full expression of the animal’s genetic potential. This concept may well be the future for animal welfare, because it highlights the need to incorporate traits related to production and robustness, simultaneously, to reach sustainable breeding goals. This review explores the identification of potential genetic markers for robustness within the hypothalamic-pituitary-adrenal axis (HPAA), since this axis plays a vital role in the stress response. If genetic selection for superior HPAA responses to stress is possible, then it ought to be possible to breed robust and easily managed genotypes that might be able to adapt to a wide range of environmental conditions whilst expressing a high production potential. This approach is explored in this review by means of lessons learnt from research on Merino sheep, which were divergently selected for their multiple rearing ability. These two selection lines have shown marked differences in reproduction, production and welfare, which makes this breeding programme ideal to investigate potential genetic markers of robustness. The HPAA function is explored in detail to elucidate where such genetic markers are likely to be found.

Relative contribution of P450c17 towards the acute cortisol response: Lessons from sheep and goats.

The rapid release of cortisol from the adrenal cortex upon ACTH receptor activation plays an integral role in the stress response. It has been suggested that the quantitative control over adrenal steroidogenesis (quantity of total steroids produced) depends on the activities of cytochrome P450 side-chain cleavage and steroidogenic acute regulatory protein that supplies pregnenolone precursor to the pathway. The qualitative control (which steroids) then depends on the downstream steroidogenic enzymes, including cytochrome P450 17α-hydroxylase/17,20-lyase (P450c17). In this review we focus on the relative contribution of P450c17 in the qualitative control of cortisol production with data collected from studies on South African Angora and Boer goats, as well as Merino sheep. Unique P450c17 genotypes were identified in these breeds with isoforms differing only with a couple of single amino acid residue substitutions. This review demonstrates how molecular and cellular differences relating to P450c17 activity can affect physiological and behavioural responses.

Spatial memory is impaired by peripubertal GnRH agonist treatment and testosterone replacement in sheep

Highlights • Peripubertal GnRHa impaired long-term spatial reference memory.• This GnRHa-effect was not counteracted with testosterone replacement in rams.• Traverse times of spatial orientation and learning tasks were unaffected by GnRHa.• GnRHa exaggerated emotional reactivity during these spatial tasks.• Testosterone replacement decreased emotional reactivity and motivation in tasks.

A reduction in long-term spatial memory persists after discontinuation of peripubertal GnRH agonist treatment in sheep

Highlights • Peripubertal GnRHa impaired long-term spatial memory.• This impairment was not reversed after discontinuing GnRHa-treatment.• Spatial orientation and learning performance remained unaffected following GnRHa withdrawal.• Speed of progression through these spatial tasks was altered after discontinuing GnRHa.• GnRH irreversibly alters these cognitive functions during critical window of development.

Alternative (backdoor) androgen production and masculinization in the human fetus

Masculinization of the external genitalia in humans is dependent on formation of 5α-dihydrotestosterone (DHT) through both the canonical androgenic pathway and an alternative (backdoor) pathway. The fetal testes are essential for canonical androgen production but little is known about the synthesis of backdoor androgens despite their known critical role in masculinization. In this study, we have measured plasma and tissue levels of endogenous steroids in second trimester human male fetuses using multi-dimensional and high-resolution mass-spectrometry. Results show that androsterone is the principal backdoor androgen in the fetal circulation and that DHT is undetectable (<1ng/ml). Backdoor pathway intermediates are found primarily in the placenta and fetal liver with significant androsterone levels also in the fetal adrenal. Backdoor intermediates, including androsterone, are mostly undetectable in the fetal testes. This is consistent with transcript levels of enzymes involved in the backdoor pathway (SRD5A1, AKR1C2/4, CYP17A1), as measured by qPCR. These data identify androsterone as the predominant backdoor androgen in the human fetus and show that it is formed primarily in non-gonadal tissue with placental progesterone the likely substrate. Masculinization of the human fetus depends, therefore, on androgen synthesis by both the fetal testes and non-gonadal tissues leading to DHT formation at the genital tubercle. Our findings provide, for the first time, a solid basis to explain why placental insufficiency is associated with disorders of sex development in humans

Circadian rhythms of melatonin and behaviour in juvenile sheep in field conditions: Effects of photoperiod, environment and weaning

Entrainment of circadian rhythms (CR) to the light dark cycle has been well described under controlled, experimental conditions. However, studies in rodents have reported that rhythms in the laboratory are not always reproduced under field conditions. The aim of this study was to characterise the CR of sheep maintained under conditions of standard UK farm animal husbandry and to investigate the effects of environmental challenges presented by season, weaning and changes in housing on CR. Male sheep (n = 9) were kept at pasture, or group housed in barns, under natural photoperiod for one year. CR in locomotor activity were monitored using accelerometry, and 24 h patterns in plasma cortisol and melatonin were measured every 4 h by ELISA. CR was measured before and after weaning, in summer and winter, and at pasture and by barn housing. Cosinor analysis revealed high amplitude, diurnal rhythms in locomotor activity that were disrupted by weaning and by barn housing. Rhythms in winter showed an interrupted night time activity pattern, but only when the sheep were kept at pasture. Cortisol and melatonin secretion followed typical circadian patterns in winter and summer. The CR of the sheep under the field conditions of this study were strikingly robust under basal conditions, but easily disrupted by environmental challenges. Interrupted patterns of activity during the long nights of wintertime, not previously reported for sheep kept in experimental conditions were recorded. Based on these findings, we propose that animals require exposure to more complex environments than the laboratory in order to exhibit their true circadian phenotype.

The Effect of Extensive Human Presence at an Early Age on Stress Responses and Reactivity of Juvenile Ostriches towards Humans

Simple Summary Husbandry practices for rearing ostriches in commercial farming environments are currently not optimized. Ostrich chicks may experience stressful episodes and fear of humans during routine farm management practices such as handling, which ultimately may impact on their welfare and explain the poor production performance observed in this species. However, extensive human presence and regular gentle handling has been demonstrated to alleviate stress sensitivity during handling by lowering the fear of humans in other species; be they kept as livestock, in a laboratory, or as pet animals. In this study, ostrich chicks exposed to extensive human presence and gentle handling showed lower stress sensitivity when handled for feather harvesting and clipping and were more inclined to associate with familiar humans at a later stage of their life compared with chicks that had limited human presence and care. This suggests that providing ostrich chicks with extensive human presence and gentle handling at a young age can assist in improving ostrich welfare. Abstract The effect of extensive human presence and regular gentle handling performed at an early age (0–3 months old) on stress responses and reactivity of juvenile ostriches towards humans was investigated. A total of 416 ostrich chicks over two years were exposed to one of three treatments for three months after hatching; namely, Human Presence 1 (HP1, N = 144): extensive/prolonged human presence with physical contact (touch, stroking), gentle human voice, and visual stimuli; Human Presence 2 (HP2, N = 136): extensive/prolonged human presence without physical contact, but with gentle human voice and visual stimuli; and the Standard treatment (S, N = 136): human presence limited to routine feed and water supply as a control. At 7.5 months of age, the plasma heterophil/lymphocyte (H/L) ratio was measured before and 72 h after feather harvesting and feather clipping to determine acute stress responses, while chronic stress was measured by quantification of corticosterone (CORT) concentrations in the floss feathers of the birds. Birds’ behavioural response towards a familiar or an unfamiliar handler was evaluated at 12 months using docility and fear tests, and through behavioural observations conducted on random days between the ages of 8–13 months. Willingness to approach, and to allow touch interactions, aggressiveness, and exhibition of sexual display towards the handler, was recorded. No difference in the H/L ratios before and after feather harvesting and clipping was observed in HP1 birds, whereas H/L ratios showed a significant increase 72 h post feather harvesting and clipping in HP2 and S birds (p < 0.05). Birds from the S treatment exhibited a significantly (p < 0.05) higher feather CORT concentration compared with HP1 birds, while HP2 birds had intermediate responses. Birds’ reactivity towards humans and temperament as evaluated using behavioural observations, docility, and fear tests was not affected by treatment (p > 0.05). However, HP1 and HP2 birds were more inclined (p < 0.05) to approach a familiar rather than an unfamiliar handler during the behavioural observations, indicating an ability to distinguish between a familiar and an unfamiliar handler. Overall, the results indicate that early gentle human interactions with ostrich chicks can be beneficial in reducing physiological stress sensitivity later in life and facilitate the ability of ostriches to distinguish between familiar and unfamiliar handlers.