# The Effect of Photoperiod on the Profile of Prolactin, Leptin, Insulin and the Content of Bioactive Substances in Sheep Milk During the Rearing Period of Lambs

## TL;DR

Longer daylight hours during lambing increase milk production and lamb growth in sheep through hormonal and nutritional changes in milk.

## Contribution

Demonstrates how photoperiod affects milk hormones, composition, and lamb growth in sheep, offering practical insights for sheep production.

## Key findings

- Ewes lambing in longer daylight periods produced milk with higher prolactin and insulin levels and higher milk yield.
- Lambs from long-day ewes had greater daily weight gains compared to those from short-day ewes.
- Milk from short-day ewes had higher dry matter, fat, protein, and lactose content.

## Abstract

Seasonal changes in day length strongly influence physiological processes in sheep, including milk production and lamb growth. This study examined how the season of lambing affects milk hormone levels (prolactin, leptin, and insulin), the nutrient composition of milk, and lamb body weight gain. Ewes that lambed under longer daylight hours produced more milk with higher prolactin and insulin levels, and their lambs showed greater daily body weight gains compared to mothers lambing under shorter daylight hours. Differences in milk nutrient content were also found between seasons. These studies demonstrate that seasonal environmental factors can alter both milk quantity and quality, thus influencing offspring growth. Understanding these effects helps improve sheep management practices, optimal planning of production seasons, and strategies that support both milk yield and lamb development, which is important for animal welfare and animal production efficiency.

Photoperiod and seasonality influence reproduction and lactation in sheep, but their effects on milk hormones, milk composition, and lamb growth are not fully understood. This study assessed the effect of season on milk prolactin, leptin, and insulin concentrations, milk chemical composition, lactation performance, and lamb growth in Polish Mountain ewes. Forty ewes were divided into the following two groups: short-day (lambing in December, n = 20) and long-day (lambing in May, n = 20). Milk samples were collected on days 5, 15, 25, 35, and 45 of lactation. Ewes in the long-day photoperiod had higher milk yield (p < 0.01) and higher prolactin and insulin concentrations (p < 0.01), whereas leptin concentrations did not differ seasonally. Milk from short-day ewes was characterized by higher dry matter and fat content (p < 0.01) and higher protein and lactose content (p < 0.05). Lambs from the long-day group achieved higher mean daily gain (p < 0.01). These results indicate that photoperiod influences lactation performance, milk composition, and offspring growth through seasonal hormonal and metabolic mechanisms, suggesting that appropriate lambing timing and day length manipulation can improve milk production efficiency and lamb growth in practical sheep production systems.