Meta-analysis of the effect of glycerin inclusion in dairy cattle diet on milk fatty acid profile

Abstract

The use of glycerin in diets for dairy cows initially emerged as an alternative for the prevention and control of ketosis. However, despite some controversy, there are still several studies associating glycerin with increases in daily milk yield, with possible changes in its constituents. Therefore, the objective of this study was to evaluate, using a meta-analysis approach, the effect of glycerin inclusion in dairy cow diets on milk fatty acid. Twenty-two peer-reviewed publications with 66 treatment means were included in data set. The effect of glycerin inclusion in diet (treatment) were evaluated using random-effect models to examine the weighted mean differences (WMD) between a control diet (without glycerin in the diet) and the treatment diet. Heterogeneity was explored by meta-regression and subgroup analysis performed for: genetic type; days in milk; experimental period; glycerin in diet; glycerin type and concentrate in diet. Inclusion of glycerin in the diet increased the digestibility of dry matter and protein, as well as ruminal propionate. It did not affect dry matter intake (P=0.351) and milk yield (P=0.730). The effect of glycerin inclusion on the milk fat yield is dependent on the genetic group, in which Holstein (WMD= -0.04 kg/d; P=0.010) and Holstein-crossbreed (WMD= -0.10 kg/d; P<.0001) cows produced less fat in milk compared to Jersey cows, when glycerin was included in the diets. Glycine inclusions of up to 100 g/kg in the diet of dairy cows did not negatively affect milk production and composition. However, inclusions above 150 g/kg of glycerin in the diet reduced the concentration of fat, and of unsaturated, monounsaturated, polyunsaturated fatty acids and conjugated linoleic acid (CLA C18: 2 cis-9 and trans-11) in milk. The results reported in our meta-analysis does not demonstrate the effectiveness of glycerin in improving the composition of milk and a group of fatty acids of importance for human health such as C18: 2 cis-9, trans-11 CLA.

Effect of Glycerol on Milk Yield, Its Quality and Blood Parameters of Holstein Cows

“…The high concentration of glucose in T2 and T3 groups may be due to the fact that the dietary glycerol is mostly absorbed directly by the rumen epithelium or the small intestine and transported through the bloodstream to the liver where the enzyme glycerol kinase converts it to glycerol-3-phosphate used to stimulate glucose formation in the liver through the process of gluconeogenesis (31,41), or due to the fermentation of glycerol by rumen bacteria to propionate, which is transferred to the liver to convert to Succinyl-CoA, which enters the Krebs cycle to turn into pyruvate phosphoenol to form glucose through the process of Gluconeogenesis (35). This result is consistent with the study of Torres et al (45) who reported that glycerol increases blood glucose concentration by 2.5%, and also the study of Goff and Horst (21), who indicated that giving milk cows with an amount of 1, 2 or 3 liters of glycerol results in an increase in blood glucose by 16%, 20%, and 25%, respectively, as glycerol is one of the precursors that form glucose from the process of gluconeogenesis in the liver (21). In addition to other studies, which showed the positive effect of glycerol in increasing blood glucose concentration in dairy cows (11,46,47).…”

“…This result is consistent with the study of Kupczynski et al (30), conducted on Holstein cows, by given 300 ml / day of pure glycerol, and the result was a decrease in the concentration of NEFA and BHBA and an increase in the serum concentration of triglycerides, indicating the positive effect of glycerol on reducing the level of NEFA and BHBA (47). Similarly, Torres et al (45) reported that glycerol increases the serum concentration of glucose in the blood by 2.5% and reduces the concentration of NEFA by 5.6%. REFERNCES…”

“…Similar, Kupczynski et al (31) reported the importance of using glycerol in the diet of ruminants to reduce production costs by replacing it with feed grains or using it as a preventive agent against metabolic problems and ketosis. Other studies indicated that the effect of glycerol on the performance and productivity of cows depends on the level and purity of glycerol added to the feed (19,26,45). Despite those and other studies that indicated the importance and role of glycerol in enhancing cow productivity, they did not indicate the qccurate level of dietary glycerol (33).…”