Performance strategies affect mammary gland development in prepubertal heifers

Area of Science:

• Animal Science
• Dairy Cattle Nutrition
• Reproductive Biology

Background:

• Holstein × Gyr (H×G) cattle are the predominant dairy breed in Brazil.
• The impact of excessive energy intake on mammary development in H×G heifers compared to purebred Holsteins is not well understood.
• Dietary energy supply during the growing period may influence mammary gland development in H×G heifers.

Purpose of the Study:

• To evaluate the effect of different average daily gains (ADG) on biometric measurements, mammary parenchyma (PAR), mammary fat pad (MFP), and blood hormones in H×G heifers.
• To determine if high energy intake negatively affects mammary development in H×G heifers.

Main Methods:

• Eighteen H×G heifers were assigned to three ADG programs: high gain (HG; 1 kg/d), low gain (LG; 0.5 kg/d), and maintenance (MA; minimal gain) over 84 days.
• Biometric measurements, blood hormone levels, and mammary tissue composition (PAR and MFP) were analyzed post-slaughter.
• Gene expression related to mammary growth and blood hormone concentrations were assessed.

Main Results:

• Heifers in the HG group exhibited the highest body weight and body condition score, while MA heifers were the smallest.
• High ADG (HG) resulted in a heavier MFP but a lower amount and percentage of PAR in the udder compared to LG and MA groups.
• PAR composition showed lower crude protein (CP) concentration and higher fat content in HG heifers, with altered gene expression related to mammary growth.

Conclusions:

• High average daily gain achieved through excessive energy intake negatively impacts mammary development in Holstein × Gyr heifers.
• Dietary energy supply during the heifer growing period significantly influences mammary gland composition and development.
• Findings suggest that managing energy intake is crucial for optimizing mammary development in H×G dairy cattle.