An insufficient glucose supply causes reduced lactose synthesis in lactating dairy cows fed rice straw instead of alfalfa hay1

Abstract

The objective of the present study was to investigate the nutrient availability for milk production in the mammary gland of lactating cows fed different forage-based diets. The 3 diets contained 30% corn stover (CS), 30% rice straw (RS), or 23% alfalfa hay plus 7% Chinese wild rye hay (AH) as a forage source. All diets contained 15% of DM as corn silage and 55% of DM as concentrate. The percentage of milk lactose was always lower in the RS-fed cows than in the cows fed AH or CS during the 12-wk feeding trial ( < 0.01). Ruminal propionate concentrations were lower in the RS group than in the AH group ( = 0.03). The ratio of insulin to glucagon in the mammary venous plasma was greater in the AH group than in the CS or RS group ( = 0.04). The abundance of the pyruvate carboxylase mRNA in the liver was lower in the RS group than in the AH or CS group ( = 0.04), and the abundance of mitochondrial phosphoenolpyruvate carboxykinase, IGF-1 receptor, and phosphofructokinase-liver, phosphofructokinase-muscle, and phosphofructokinase-platelet mRNA in the liver were lower in the RS group than in the AH group ( < 0.05). The mammary glucose uptake was greater in the AH-fed cows than in the CS- or RS-fed cows ( = 0.02). The mRNA abundance of the glucose transporters in the mammary gland was similar among the 3 treatments. The mRNA abundance of α-lactalbumin in the mammary gland of the cows fed RS tended to be greater compared with that of the cows fed AH or CS. The milk potassium concentration was greater in the cows fed RS than those fed AH or CS ( < 0.01). In summary, the insufficient ruminal propionate concentrations in the cows fed RS were associated with lower gluconeogenesis in the liver, resulting in the shortage of glucose supply for mammary utilization.

Field findings about milk ethanol stability: a first report of interrelationship between α‐lactalbumin and lactose

“…Consequently, lactose usually appears in smaller amounts in unstable milk,, while the average levels of chloride, sodium and potassium are higher . Wang et al . also stated that the lower milk osmolarity in response to reduced milk lactose concentration could be compensated by higher milk K + concentration.…”

“…Consequently, lactose synthesis is dependent upon: (i) the α‐LA:galactosyltransferase ratio; (ii) the expression of α‐LA through genic expression; and (iii) the arterial glucose supply to the mammary gland . This may hold true, as feed restriction of dairy cattle – namely, a factor that critically deprives glucose supply to the mammary gland – has already been associated with alcoholic instability of milk .…”

Low‐quality rice straw forage increases the permeability of mammary epithelial tight junctions in lactating dairy cows

“…Nevertheless, multiple indicators showed leaky tight junctions in cows fed RS. This tight junction with greater permeability might have resulted from the lower metabolic energy supply in these animals . Limitations on the dietary energy supply to the mammary gland can lead to mammary cell turnover, remodeling, and increased permeability of the tight junction in lactating dairy cows as observed in previous studies …”

“…The higher lactose concentrations in RS‐fed cows suggested a higher mammary permeability, compared with AH‐fed animals in this study. Although the milk K + concentration showed no difference in the two diets, which could be due to the relatively high K + concentration in the RS diet, the higher milk Na + , Na + /K + ratio, BSA, and plasmin and higher plasma lactose all indicated a higher permeability of tight junction in the mammary glands of cows fed RS. Because some serum albumin in milk may be synthesized in mammary epithelial tissues, caution should be exercised when using milk albumin as a biomarker for mammary permeability.…”

“…Other studies suggest that leaky tight junctions in the mammary gland can be repaired by the injection of hormones, such as cortisol or prolactin, through increasing metabolic glucose availability . In our previous study, we observed that the milk of rice straw‐fed cows had a higher Na + concentration than that of alfalfa‐fed cows, and there was a deficiency of metabolic glucose supply in rice straw‐based diet . Thus, we hypothesized that low‐quality forage‐based diets may increase the permeability of mammary epithelial tight junctions by affecting mammary epithelial cell proliferation/apoptosis.…”