Analysis of the effects of thermal stress on milk production in a humid tropical climate using linear and non-linear models.

The decline of milk production in crossbred cattle during the onset of summer was evaluated using lactation records of the cows (n = 48) maintained at the Livestock Research Station, Thiruvazhamkunnu, for the period between January 2019 and March 2019. Climate data were obtained from an automatic weather station maintained on the campus. The temperature-humidity index (THI) was used to assess the thermal stress on animals. Values varied between 70.78 and 83.93 during the study period, indicating that the cows were exposed to mild and moderate stress. Highly significant negative correlations (p < 0.01) were observed between the average temperature, THI, and milk production. Linear, logarithmic, power, and polynomial models linking milk production and THI were used to fit the data. The coefficient of determination (R2) in general exceeded 0.85 and these equations could be used to model the drop in milk production or predict production loss due to thermal stress. The rate of decline in daily milk production observed in the study was 2.13% per unit increase in THI. A general linear model that included THI, parity, and the stage of lactation as independent variables, and milk production as a response variable, was also tested. Parity and stages of lactation were observed to influence forenoon and afternoon milk production significantly (p < 0.01). The temperature-humidity index also had a significant effect on forenoon milk production (p < 0.05) and afternoon milk production (p < 0.01).

Relative abundance of tissue mRNA and association of the single nucleotide polymorphism of the goat NGF gene with prolificacy.

Nerve Growth Factor (NGF) promotes the development of pre-antral ovarian follicles through ovarian innervations and regulation of ovarian response to gonadotropins. The present study was conducted to study the tissue gene expression profile, to characterize the genetic variants, find associations of the NGF gene with prolificacy in the prolific Malabari and less prolific Attappady Black goats because NGF has an important role in reproduction by augmenting ovarian folliculogenesis. Relative abundance of NGF mRNA was greatest in reproductive tissues signifying its role in reproduction. The PCR-SSCP analysis of a 251bp fragment of Exon 3 of the NGF gene from the 277 goats revealed four diplotypes (EE, EF, FF and EG) with respective frequencies of 0.76, 0.22, 0.01 and 0.01. Sequencing of the representative samples revealed one synonymous and one novel non synonymous mutations (g.705G>A and g.715C>T). Statistical analysis indicated that the SNP g.705G>A was associated with litter size in Attappady Black goats (P<0.05) and a PCR-RFLP was designed using the restriction enzyme, BpiI, for rapid screening of the SNP. The results of the present study suggest that the NGF gene is a primary candidate gene affecting prolificacy in goats and may be used for Marker Assisted Selection (MAS) in goats, especially in lowly prolific Attappady Black goats.