# Dietary Protein Level in Late Gestation: Effects on Nutritional and Developmental Responses in Jennies and Their Foals

## TL;DR

Moderate protein diets during late gestation in donkeys improve nutrient digestion and foal growth without extra benefits from high protein.

## Contribution

Identifies optimal moderate protein levels for gestating donkeys to enhance productivity and foal development.

## Key findings

- Moderate protein diets (11.52% CP) improved nutrient digestibility and foal growth compared to low protein.
- High protein diets (12.48% CP) did not provide additional benefits in nutrient utilization or productivity.
- Low protein diets led to greater postpartum weight loss in jennies compared to high protein diets.

## Abstract

This study investigated the effects of dietary protein levels on body weight changes during late gestation, nutrient digestion, serum parameters in jennies, and foal growth and development. The results indicate that a moderate protein level provides optimal balance: it enhances nutrient digestion, maintains healthy serum parameters, assists jennies in retaining better body condition postpartum, and promotes increased foal birth weight and growth development. These findings hold significant theoretical and practical implications for improving protein nutrition in gestating donkeys, enhancing jennies’ productivity and foal growth performance, thereby boosting profitability in donkey breeding and rearing operations.

This study evaluated the effects of dietary protein levels during late gestation on nutrient digestibility, plasma amino acid profiles in jennies, and donkey foal growth performance. Twenty-four pregnant jennies were randomly assigned to one of three diets with different crude protein (CP) contents during late gestation: 12.48% (HP), 11.52% (MP), and 10.54% (LP) on a dry matter basis. All animals received the same diet immediately after parturition for a duration of 30 days. During the trial, two digestion experiments were conducted, blood samples were collected at 28 and 7 days prepartum, and weekly weight measurements of jennies and foals were recorded. The results indicated that the dietary protein level did not significantly affect feed intake in late gestation. However, apparent nutrient digestibility of dry matter (DM), neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), and ether extract (EE), and calcium (Ca) and phosphorus (P) was generally higher in the MP and LP groups than in the HP group, with MP showing the most consistent improvements across nutrients and timepoints (p < 0.05). Although the HP diet increased plasma concentrations of certain amino acids, including glutamic acid (Glu), valine (Val), methionine (Met), leucine (Leu), essential amino acids (EAAs), functional amino acids (FAAs), and branched chain amino acids (BCAAs), and elevated serum levels of glucose (GLU), blood urea nitrogen (BUN), and creatinine (CRE), it failed to improve postpartum weight recovery in jennies, highlighting that weight dynamics during this period are governed by factors beyond dietary protein content alone. Specifically, the LP group exhibited significantly higher cumulative postpartum weight loss over weeks 1–4 than the HP group (p = 0.004). Regarding offspring performance, both HP and MP diets improved foal birth weight, weekly body weight up to 4 weeks, average daily gain, and body height compared to the LP group (p < 0.05), with no significant differences observed between the HP and MP groups. In conclusion, for jennies under the current confined feeding system, a late-gestation diet containing 11.52% CP was adequate to support higher nutrient digestibility in the jennies and better growth performance in their foals, compared to a lower protein level (10.54% CP). However, increasing the dietary CP to 12.48% provided no additional benefits in nutrient utilization or overall productivity.