Effect of melatonin implants on the incidence and timing of puberty in female red deer (Cervus elaphus)

Comparison of the accumulation of macro- and microelements in the bone marrow and bone of wild and farmed red deer (Cervus elaphus)

Background

The cells of the entire body, including the skeletal system, especially of young animals, may derive from the bone marrow in which they multiply. Therefore, it is important to assess whether the diet and quality of life of deer have a significant impact on the elemental composition of bone and bone marrow, which can directly affect their health and growth. The aim of this study was to determine the concentrations of macro- (Ca, calcium, P, phosphorus, Mg, magnesium, K, potassium, Na, sodium) and microelements (Li, lithium, Cr, chromium, Mn, manganese, Co, cobalt, Cu, copper, Zn, zinc, Se, selenium, Mo, molybdenum, and Sn, tin) accumulated in the bone marrow and bones of deer (Cervus elaphus). The study was carried out on 15 young stags divided into two groups: farmed and wild animals. The concentrations of macro- and microelements were analysed using the inductively coupled plasma mass spectrometry technique. This research expands our knowledge on this topic, which so far has not been extensively studied.

Results

The mean content of K, Na, Zn and Se in the bone marrow of farmed animals was significantly higher than in wild deer, whereas the mean content of Ca, P, Mg, K, Na and Li in the bones was higher in wild animals than in farmed individuals (p < 0.05). In addition, the mean concentration of Cr, Mn, Cu, Se and Mo in the bones of the analysed animals differed significantly (p < 0.05) and was higher in the farmed deer. The mean concentration of Se in the bone marrow of wild deer decreased with the increase of the body weight (p < 0.05). In turn, the mean content of Mn in the bone marrow and of Mo in the bones of the animals was significantly positively correlated with the animals’ body weight (p < 0.05).

Conclusions

The obtained results indicated different levels of micro- and macro-components in the body of farmed and wild deer, though without clear and strong variations. Generally, the higher level of macronutrients in the bones of wild deer may be related to the higher physiological importance of these minerals for life activities in the natural environment and to the limited supply of balanced food. On the other hand, the higher levels of microelements in the tissues of farmed animals may result from their significantly better nutritional status in the first year of life, achieved through appropriate nutrition as well as diet supplementation of adult females.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03041-2.

Exogenous Melatonin Improves the Reproductive Outcomes of Yearling Iberian Red Deer (Cervus elaphus hispanicus) Hinds

Simple Summary

Increasing the reproductive performance of hinds is considered to be a key factor of overall farm deer productivity. In the case of yearling hinds, this aspect becomes more important, as a delay in the pubertal onset will compromise the reproductive performance of the entire herd (decreased fertility), and these yearling hinds will carry this ‘late’ condition throughout their reproductive life. The aim of this study was to explore the use of melatonin implants on yearling Iberian red deer (Cervus elaphus hispanicus) hinds to improve their fertility outcomes, advance the calving date and the calves’ weight, and to prevent the negative impact of yearling hinds’ low liveweight on their reproductive outcomes. Melatonin implants (18 mg), administered three-fold (two implants each time) every 30 days before the breeding season, rendered significantly higher fertility rates (regardless of the yearling hind’s weight) and heavier calves, and advanced the calving date in the yearling hinds by 15 days compared to non-treated hinds. In addition, halving the number of yearling hinds that received melatonin provided a similar benefit to a large-scale treatment of the whole herd, which indicates female-to-female stimulation of the ovarian activity. Taken together, this protocol for melatonin treatment simplifies its administration, reduces its costs, and assures the enhancement of the reproductive productivity of the entire farm.

Abstract

The aim of this study was to assess the effect of melatonin implants on the reproductive performance of yearling Iberian red deer (Cervus elaphus hispanicus) hinds. It also explored exogenous melatonin administration as a tool to minimize the negative effect of a low yearling hind’s liveweight on their reproductive efficiency. In addition, the effect of melatonin-treated yearling hinds on non-treated hinds was studied in order to provide a practical and economical protocol to improve farms’ productivity. A total of 4520 Iberian red deer hinds belonging to the same farm were included in this study. Melatonin (108 mg/hind) implants were administered three-fold every 30 days before the breeding season. Fertility rates, calves’ weights and calving dates were registered for each hind. The results showed that exogenous melatonin increased significantly (p < 0.05) the calves’ weight (32.39 ± 1.07 kg vs. 27.65 ± 1.11 kg for Weight 1_calf (July) and 46.59 ± 1.50 kg vs. 41.79 ± 1.54 kg for Weight 2_calf (August, at weaning)) and advanced the calving date by 15 days in yearling hinds compared to the non-treated group. In addition, the administration of melatonin implants before the breeding season was able to minimize the negative effect of low yearling hinds’ liveweight (Weight 1_hind) on their future reproductive outcomes, as the fertility rates increased by 46% and the calves’ weight increased by 7 kg after the melatonin treatment, regardless of the yearlings’ weight. Finally, when both experimental groups (melatonin and non-treated) were kept separate, higher fertility rates (76.73 ± 7.18% vs. 66.94 ± 7.41%) were observed for the melatonin-treated hinds compared to the non-treated hinds. However, when both groups of yearling hinds were maintained together, no significant differences were observed in their fertility outcomes (78.13 ± 21.26% vs. 78.12 ± 23.32%). Therefore, melatonin implants may be used in yearling Iberian red deer hinds as a management tool to improve their reproductive productivity.

Effects of supplementation with different levels of calcium and phosphorus on mineral content of first antler, bone, muscle, and liver of farmed fallow deer (Dama dama)

Nutrition is one of the main factors influencing physiological processes, e.g., growth and antler development, in Cervidae. The aim of this study was to demonstrate a possible effect of supplementation with different levels of calcium (Ca) and phosphorus (P) on the mineral composition of antlers and bones, and its effect on the content of macroelements — Ca, potassium (K), magnesium (Mg), sodium (Na), and P — in the muscle tissue, liver, and blood of farmed fallow deer fawns. The results show a positive effect of increased doses of Ca and P on body weight at the age of 14 mo. Additionally, there was a significant increase in the content of Ca, Mg, Na, and P in antlers and Ca, Na, and P in bones. The muscle tissue was characterised by a significant increase only in the content of Na, whereas Ca, K, and P levels increased significantly in the liver. In turn, the serum P content decreased significantly. Adequate Ca and P supplementation exerts a positive effect on the mineral composition of bones and whole antlers of farmed fallow deer fawns, and it enhances the concentrations of macroelements in tissues, which may constitute a reservoir used for future development of antlers. It also has a positive effect on body weight.

Impacts of nutrition on reproduction in female red deer: phenotypic flexibility within a photoperiod-mediated seasonal cycle

Red deer (Cervus elaphus) are widely distributed throughout cold northern temperate latitudes, where they have evolved to cope within highly seasonal continental environments. Naturalisation of red deer to the more moderate seasonal (but variable climatic) environment of New Zealand has been spectacularly successful, and they are widely farmed in the country’s pastoral environment for venison and antlers. The species is genetically programmed to exhibit photoperiodic control of voluntary feed intake, growth and reproduction, ensuring that energy demands are aligned with seasonally available resources and offspring are born in summer when climate is favourable for survival. However, despite genetic control of their endogenous seasonal cycles, there appears to be a strong ability for environmental factors such as nutrition to generate large phenotypic variation of seasonal traits. This may have contributed to their successful naturalisation to a wider range of seasonal environments than would be expected within their ancestral range. While precise timing of conception and duration of gestation length are the two fundamental mechanisms by which the strict seasonality of birth is maintained in seasonally breeding mammals, red deer exhibit considerable variation in both these traits. The present paper examines the outcomes of recent studies on farmed red deer on the impacts of lactation on conception date, the influence of nutrition during pregnancy on gestation length, and early life growth effects on the onset of female puberty. These studies have collectively demonstrated that while red deer are assumed to be under fairly rigorous genetic control of seasonality traits, they have a repertoire of phenotypic variation at various points of the reproductive cycle that may potentially allow a degree of adaptation to climatic variation that influences annual feed supply. This may explain the success of red deer in colonising a range of new environments that differ seasonally from their ancestral environment.

Investigation of Toxoplasma gondii and association with early pregnancy and abortion rates in New Zealand farmed red deer (Cervus elaphus)

This study tested for association between Toxoplasma gondii and pregnancy and abortion to investigate sub-optimal reproduction in farmed red deer (Cervus elaphus). Sera from a sub-sample (n = 2304) of pregnant and non-pregnant hinds in early gestation at first pregnancy scan (scan 1) and approximately at the end of second trimester at second pregnancy scan (scan 2) were tested for T. gondii antibodies using a validated ELISA. Foetuses and/or uteri from pregnant, non-pregnant, and aborting hinds at scan 1, scan 2, or weaning were tested for T. gondii DNA by nested PCR. At scan 1, 31.1% of 861 rising two-year-old (R2) and 28.3% of 357 mixed-aged (MA, ≥ 2 years) hinds were sero-positive. There was no association between scan 1 serology and non-pregnancy at animal (R2, p = 0.05 and MA, p = 0.43) or herd level (R2, p = 0.37). Toxoplasma gondii DNA was detected in 3/18 placenta and 4/18 foetal brains from aborting R2 hinds and 15/157 R2 and 3/21 MA uteri from non-pregnant hinds at scan 1. At scan 2, sero-prevalence was higher (odds ratio = 1.6, 95% CI = 1.04-2.48) in aborted (34.3% of 268) than in non-aborted (23.5% of 446) R2 hinds (p = 0.03) and 7.9% of abortions between scans were attributable to T. gondii exposure. Within-herd sero-prevalence at scan 2 was positively associated with daily abortion rate in R2 herds with aborted hinds (p < 0.001) but not in MA herds (p = 0.07). Toxoplasma gondii DNA was detected in 27/169 uteri, 2/20 cotyledons, and 1/5 foetal brains from aborted hinds at scan 2 and in uteri from 5/33 hinds not rearing a calf to weaning. Toxoplasma gondii RFLP genotyping of five loci revealed a unique type I/III genotype pattern, TgRDNZ1, in a foetal brain sample, not been previously reported in deer. These findings provide serological and molecular evidence that T. gondii infection is associated with abortion in red deer, possibly in all three trimesters.

Investigation of association between bovine viral diarrhoea virus and cervid herpesvirus type-1, and abortion in New Zealand farmed deer

This study tested for association between bovine viral diarrhoea virus (BVDv) and cervid herpesvirus type-1 (CvHV-1) exposure and abortion in New Zealand farmed red deer. Rising two-year-old (R2, n = 22,130) and mixed-age (MA, n = 36,223) hinds from 87 and 71 herds, respectively, throughout New Zealand were pregnancy tested using ultrasound early in gestation (Scan-1) and 55-89 days later (Scan-2) to detect mid-term abortion. Sera from aborted and non-aborted hinds at Scan-2 were tested for BVDv and CvHV-1 using virus neutralisation tests. Available uteri from aborted hinds and from hinds not rearing a calf to weaning were tested by PCR for herpesvirus DNA. In herds with aborted hinds, 10.3% of 639 R2 and 17.2% of 302 MA hinds were sero-positive for BVDv and 18.6% of 613 R2 and 68.5% of 232 MA hinds were sero-positive for CvHV-1. There was no association between BVDv sero-status and abortion at animal level (R2 p = 0.36, MA p = 0.76) whereas CvHV-1 sero-positivity was negatively associated with abortion in MA hinds (p = 0.01) but not in R2 hinds (p = 0.36), MA). Eleven of 108 uteri from aborted R2 hinds but no MA hinds were positive for herpesvirus DNA. Vaginal samples from four R2 and one MA aborted hinds tested were negative for herpesvirus DNA. A Cervid Rhadinovirus type-2 (CRhV-2) was identified in seven PCR positive uteri samples. Findings suggest that BVDv and CvHV-1 may not be associated with abortion in R2 hinds, but association needs to be tested further in MA hinds. The role of CRhV-2 requires clarification.

The relationship between body-mass and puberty in young red deer (Cervus elaphus) hinds: evidence of early-life effects on permissive live-weight thresholds

This study, based on the analysis of growth and reproductive records of 6158 young red deer hinds, tested the hypothesis that the nutritional environment in early life influences the permissive body mass threshold for puberty at around 16 months of age. Live-weight at 3 months (i.e. weaning weight) was a proxy for their nutritional environment between birth and weaning, live-weight at 14 months was the indicator of pre-mating body mass, and pregnancy status at 18-19 months was a proxy for entry into puberty. Data were obtained for two sub-populations of hinds, the commercial stud herds, across four consecutive years. The modelled relationships between pre-mating live-weight and the predicted pregnancy rate demonstrated between-year variation for the logistic curves for the commercial herd for the live-weight range from 50 to 90 kg (P<0.001). For the stud herd, the predicted pregnancy rate at any given live-weight did not vary significantly between years (P>0.05) and the pregnancy rates for live-weights <90 kg were higher than for the commercial herd. The regression of average weaning weight on probability of pregnancy showed significant positive associations (P<0.05) at 60 kg, 70 kg and 80 kg (R(2)=0.513, 0.517 and 0.439, respectively). There were no significant regressions at pre-joining live-weights at 90 kg or above (P>0.05). The study supports the central hypothesis of early-life influences on the permissive body mass threshold for entry into puberty.