Influence of dietary fat on some metabolic responses of cattle to fasting

Impaired alveolar-arterial oxygen transfer is associated with reduced milk yield in primiparous post-partum dairy heifers at moderate altitude

Domestic cattle have limited cardiopulmonary reserve for their body size and oxygen requirements. Therefore, it is plausible that impaired alveolar-arterial gas exchange may be detrimental to energetically expensive traits such as milk production which, like all aerobic processes, requires oxygen. The degree of alveolar-arterial oxygen transfer impairment can be determined by estimating the alveolar-arterial oxygen (A-a O2) pressure gradient from arterial blood-gas tensions. The degree of oxygen transfer impairment is proportional to the A-a O2pressure gradient: the higher the A-a O2pressure gradient the less oxygen is transferred to the blood for a given ventilation rate. In this study two cohorts of Holstein-Friesian heifers were followed on one northern Colorado dairy farm. Arterial blood-gas analyses were performed up to 9 d post-calving. Heifers were grouped into quartiles based on A-a O2pressure gradient so that relative comparisons could be made. Heifers in the lowest (Q1) and highest (Q4) quartile had the least and greatest impairment of alveolar-arterial oxygen transfer, respectively. We hypothesised that milk yield over 60 d would be greatest for heifers in Q1and would decrease with quartile increments. Hyperventilation, as indicated by hypocapnia, was notable. Despite hypoxia, haematocrit was low. Alveolar-arterial O2pressure gradient was associated with milk production (P=0·03) when controlling for cohort, treatment for disease and calving difficulty score. Heifers in Q1produced 1992 kg (95% CI=1858, 2127 kg) of milk when controlling for all other variables. Relative to heifers in Q1, heifers in Q2, Q3and Q4produced 130 kg (95% CI=313, −52 kg; P=0·45), 285 kg (95% CI=474, 96 kg; P=0·004) and 169 kg (95% CI=395, −57 kg; P=0.14) less milk, respectively. In conclusion, efficacy of alveolar-arterial oxygen transfer was associated with milk yield in dairy heifers on one farm at moderate altitude.

Physiological and metabolic effects of prophylactic treatment with the osmolytes glycerol and betaine on Bos indicus steers during long duration transportation

The physiological and metabolic effects of prophylactic treatment with osmolytes were investigated using twenty-four 2.5-yr-old Bos indicus steers. Animals were allocated to 1 of 4 treatment groups: 1) control, feed and water deprived for 48 h (n = 6); 2) transported, transported for 48 h (n = 6); 3) glycerol, dosed with glycerol (2 g/kg of BW) and then transported for 48 h (n = 6); and 4) betaine, dosed with betaine (0.25 g/kg of BW) then transported for 48 h (n = 6). Body water, electrolytes, blood pH and gases, plasma lactate, glucose, albumin, total protein, anion gap, strong ion difference, total weak acids, and BW were determined at the conclusion of 24 and 48 h of transportation. The glycerol group had greater body water volumes than the control (P = 0.05) and transported (P = 0.02) groups. The glycerol, transported, and betaine groups had lower (P = 0.02) plasma Mg concentrations than the control group at 24 h, whereas the glycerol group maintained lower (P = 0.04) plasma concentrations of Ca than the control group. The betaine group had lower (P = 0.04) hematocrit than the control group at 24 and 48 h. Plasma bicarbonate and pCO2 were 13 and 17% greater (P = 0.01 and 0.04, respectively) in the glycerol group at 24 h compared with control and transported groups. However, the ratio of [HCO3]/[CO2] in the glycerol group did not differ from the other groups and thereby maintained pH. The glycerol group maintained a 30% greater (P < 0.001) plasma concentration of glucose than the control group, and 14% greater (P = 0.05) than the transported and betaine groups. In contrast, betaine had little effect on increasing blood glucose compared with glycerol. Glycerol-linked hyperhydration at 24 h may not only help to conserve water loss during long distance transportation, but the increased blood glucose may have an important protein-sparing effect due, in part, to greater insulin concentrations inhibiting the breakdown of muscle proteins, thus, countering the amino-acid mobilizing effect of cortisol after 24 h. Therefore, the osmolyte glycerol shows promise as a prophylactic treatment for attenuating the effects of long distance transportation by maintaining body water, decreasing the energy deficit, and preserving health and muscle quality.

Influence of dietary fat on some metabolic responses of cattle to hyperthermia induced by heat exposure

1. Two breeds of cattle which differ in their plasma concentrations of lipid components (PCLC) and ability to tolerate heat were used to study metabolic responses to hyperthermia. Two maintenance diets, LF (2.5% Fat) and HF (9.2% Fat), which were isonitrogenous and isocaloric were used. 2. The PCLC, the net esterification of cholesterol by the lecithin: cholesterol acyl transferase system and faecal fat excretion were increased by the HF diet which reduced urinary N loss. 3. Hyperthermia disturbed lipid metabolism in all animals and reductions in the concentrations of plasma cholesterol and phospholipid paralleled the increases in the quantities of fat excreted in the faeces. 4. Within breeds the animals on the HF diet maintained a higher PCLC, lower body temperature and conserved more body nitrogen during hyperthermia than animals on the LF diet. 5. The results point to a role for dietary lipid in ameliorating the metabolic disturbances in animals during chronic hyperthermia.