Effects of prepubertal growth rate and diet on lipid metabolism in lactating Holstein cows

Effects of high-grain diet feeding on fatty acid profiles in milk, blood, muscle, and adipose tissue, and transcriptional expression of lipid-related genes in muscle and adipose tissue of dairy cows

BACKGROUND

High-grain (HG) diets affect lipid metabolism in the liver and mammary tissue of dairy cows, but its effects on muscle and adipose tissue have not been wide evaluated. Thus, the aim of this study is to clarify this issue.

METHODS

Twelve Holstein cows were randomly divided into two groups: conventional diet group (CON, n = 6) and the HG diet group (n = 6). On day 7 of week 4, rumen fluid was sampled to measure pH, milk was sampled to measure components, and blood was sampled to measure biochemical parameters and fatty acid composition. After the experiment, cows were slaughtered to collect muscle and adipose tissue for fatty acid composition and transcriptome analysis.

RESULTS

HG feeding decreased the ruminal pH, milk's fat content and long-chain fatty acid proportion (P < 0.05) and increased the proportion of short- and medium-chain fatty acids in the milk (P < 0.05) as compared with CON diets. The concentrations of blood cholesterol, low-density lipoprotein, and polyunsaturated fatty acids in the HG cows were lower than those in CON cows (P < 0.05). In muscle tissue, HG feeding tended to increase the triacylglycerol (TG) concentration (P < 0.10). Transcriptome analysis revealed changes in the biosynthesis of the unsaturated fatty acids pathway, the regulation of lipolysis in the adipocytes pathway, and the PPAR signalling pathway. In adipose tissue, HG feeding increased the concentration of TG and decreased the concentration of C18:1 cis9 (P < 0.05). At the transcriptome level, the fatty acid biosynthesis pathway, linoleic acid metabolism pathway, and PPAR signalling pathway were activated.

CONCLUSION

HG feeding leads to subacute rumen acidosis and a decreased milk fat content. The fatty acid profiles in the milk and plasma of dairy cows were changed by HG feeding. In muscle and adipose tissue, HG feeding increased TG concentration and up-regulated the expression of genes related to adipogenesis, while down-regulated the expression of genes related to lipid transport. These results complement our knowledge of the fatty acid composition of muscle and adipose tissue in dairy cows and expand our understanding of the mechanisms by which HG diets affect lipid metabolism in muscle and adipose tissue.

Growth targets and rearing strategies for replacement heifers in pasture-based systems: a review

Dairy heifer growth and liveweight at first calving are regarded as important management variables affecting profitability and animal welfare. However, the appropriateness of heifer growth rate targets for different farming systems is not clear. Retrospective assessments of the association between heifer liveweight and subsequent productivity indicate significant benefits in milk production and, even, reproduction from increasing liveweight at breeding and first calving. However, prospective interventionist experiments do not concur, with very variable effects of liveweight at breeding on milk production and with only limited evidence of a positive effect of first-calving liveweight on first-lactation milk yield. In addition, any benefit in the first lactation is not evident in subsequent lactations in the limited number of long-term studies reported. Pre-weaning nutrition and average daily weight gain are areas of increasing interest, with lifelong increases in milk production resulting from accelerated growth rates during the first 8 weeks of life, indicating a possible significant return from a short-term investment. This could be one reason for the inconsistent effects of heifer liveweight at breeding and first lactation on milk production. Although the effect of pre-weaning average daily gain on heifer liveweight is short-lived, a recent meta-analysis indicated that pre-weaning average daily gain explains 22% of the variation in first-lactation milk production. Whether these differences in animal physiology have relevance in grazing systems, wherein heifers and cows do not consume sufficient nutrients to reach their potential, requires investigation. Despite considerable extension efforts over successive decades, current evidence indicates that failure to provide the new-born calf with sufficient high-quality colostrum is common. To understand the reasons for suboptimal colostrum feeding requires social research, with appropriate extension strategies developed to elicit practice change. Although there can be little doubt regarding the importance of heifer rearing to the profitability and sustainability of the farming business, the collective literature points to a failure of retrospective analyses in determining the cause of poor heifer performance. In reality, it is likely to be a combination of factors. The objective of this review is to investigate the effect of liveweight gain at various stages of the growth cycle of the heifer on the milk-production capacity of the lactating animal.

Nutrition-induced Changes of Growth from Birth to First Calving and Its Impact on Mammary Development and First-lactation Milk Yield in Dairy Heifers: A Review

This review focuses on the nutritional effects from birth until age at first calving on growth, mammary developmental changes, and first-lactation milk yield in heifer calves. The advancement in the genetic potential and the nutritional requirements of the animals has hastened the growth rate. Genetic selection for high milk yield has suggested higher growth capacity and hence increasing nutritional inputs are required. Rapid rearing by feeding high energy or high concentrate diets not only reduces the age of sexual maturity but also lowers the time period of attaining the age of first calving. However, high energy diets may cause undesirable fat deposition thereby affecting future milk yield potential. Discrepancies exist whether overfed or overweight heifers at puberty can influence the mammary development and future milk yield potential and performance. The data on post-pubertal nutritional management suggested that body weight at calving and post-pubertal growth rate is important in first lactation milk yield. There is a continuous research need for strategic feeding that accelerates growth of dairy heifers without reduction in subsequent production. Nutritional management from birth, across puberty and during pregnancy is critical for mammary growth and for producing a successful cow. This review will mostly highlight studies carried out on dairy breeds and possible available opportunities to manipulate nutritional status from birth until age at first calving.

Effect of Feeding Level Pre- and Post-Puberty and Body Weight at First Calving on Growth, Milk Production, and Fertility in Grazing Dairy Cows

The effect of feeding to achieve differential growth rates in Holstein-Friesian (HF; n = 259) and Jersey (n = 430) heifers on time to puberty and first lactation milk production was investigated in a 3 x 2 factorial design. Holstein-Friesian and Jersey calves were reared to achieve a BW of 100 and 80 kg, respectively, at 100 d. At target weight, all calves were randomly allocated to one of 3 feeding treatments to achieve different growth rates. Holstein-Friesian and Jersey calves were fed fresh pasture to achieve average daily growth rates of 0.77, 0.53, or 0.37 kg of BW/d (HF) and 0.61, 0.48, or 0.30 kg of BW/d (Jersey), respectively. Period 1 (prepubertal) was imposed until HF and Jersey treatment groups averaged 200 and 165 kg of BW, respectively. Following period 1, HF and Jersey calves from each treatment group were randomly allocated to one of 2 feeding treatments to achieve average daily growth rates of 0.69 or 0.49 kg of BW/d (HF) and 0.58 and 0.43 kg of BW/d (Jersey), respectively. Period 2 (postpubertal) was imposed until 22 mo, when heifers were returned to their farms of origin. Body weight, body condition score, height, heart girth circumference (HGC), milk production, and fertility-related data were collected until the end of the third lactation. Time to reach puberty was negatively associated with level of feeding, and heifers attained puberty at the same BW (251 +/- 25.4 and 180 +/- 24.0 kg for HF and Jersey heifers, respectively). Heifers on high feed allowances during periods 1 and 2 were heavier, taller, and had greater HGC than their slower grown counterparts until 39 mo of age when height and HGC measurements stopped. Body weight differences remained until 51 mo, when measurements ceased. High feed allowance during period 1 (prepubertal) did not affect milk production during the first 2 lactations, but did reduce milk production in lactation 3. It is possible that the expected negative effect of accelerated pre-pubertal growth was masked by greater calving BW, as BW-corrected milk yield declined in both breeds with increasing prepubertal feed allowance. Growth rate during period 2 was positively correlated with first lactation milk production. Milk yield increased 7% in first lactation heifers on the high feed allowance, which resulted in higher growth rate during period 2. Milk production during subsequent lactations was not affected. Results suggest that accelerated prepubertal growth may reduce mammary development in grazing dairy cows, but this does not affect milk production in early lactations because of superior size. Body weight at calving and postpubertal growth rate management are important in first lactation milk production, but do not affect milk production in subsequent lactations.

Milk fat depression, the glucogenic theory, and trans-C18:1 fatty acids

Metabolic and endocrinological characteristics were compared for cows that differed in the extent of milk fat depression. Forty-one multiparous Holstein cows were fed control (40% concentrate and 60% forage) and high concentrate (80% concentrate and 20% forage) diets in a doubale-reversal design. Cows showing one or more percentage units of depression in milk fat were arbitrarily classified as responders (n = 26); those remaining were classified as nonresponders (n = 15). Compared with nonresponders, responders had greater increases in DMI, estimated NEL intake and balance, BW, milk yield, protein and lactose yields in milk, weight percentage of trans-C18:1 fatty acids in milk, and concentrations of triiodothyronine and thyroxine in serum when switched from the control diet to the 80% concentrate diet. Lack of an increase in concentrations of glucose and insulin in serum of cows with the greatest decline in percentage of milk fat casts doubt on the ability of the glucogenic theory to explain milk fat depression completely.