1499
Effects of supplementation with propylene glycol in heat-stressed dairy goats
We hypothesized that supplementation with propylene glycol would increase blood glucose and spare amino acids for milk protein synthesis rather than glucose production. To test this hypothesis, we used 8 multiparous Murciano-Granadina dairy goats (40.8 ± 1.1 kg BW; 84 ± 1 DIM) individually kept in metabolic cages. The design was a replicated 4 × 4 Latin square of 4 periods; 21 d each (14 d adaptation, 5 d for measurements). Goats were allocated to one of 4 treatments in a 2 x 2 factorial arrangement. Factors were no propylene glycol (C) or 5% of Propylene glycol (PG), and thermal neutral (TN; 15 to 20°C) or heat stress (HS; 12 h/d at 37°C and 12 h/d at 30°C) conditions. This resulted in 4 treatment combinations: TN-C, TN-PG, HS-C, and HS-PG. Feed intake, milk yield, milk composition, and blood parameters were measured. No significant interaction was detected between ambient temperature and PG effects. Compared to TN, HS goats had lower feed intake, FCM, and milk contents of fat, protein and lactose. The PG increased blood glucose and insulin, but decreased DMI, blood NEFA and β-hydroxybutyrate, resulting in lower milk fat with no change in milk protein content. In conclusion, supplementation of heat-stressed dairy goats with propylene glycol did not affect milk yield or milk protein content, and caused milk fat depression syndrome.
Item |
Treatment |
SEM |
P < |
||||
TN-C |
TN-PG |
HS-C |
HS-PG |
Temp.1 |
PG |
||
DMI, Kg/d |
2.34 |
2.18 |
1.59 |
1.38 |
0.09 |
0.001 |
0.060 |
Milk yield, L/d |
1.86 |
1.80 |
1.79 |
1.66 |
0.18 |
0.210 |
0.258 |
3.5% FCM2, L/d |
2.12 |
1.78 |
1.85 |
1.48 |
0.16 |
0.001 |
0.001 |
Milk composition, % |
|
|
|||||
Fat |
4.43 |
3.46 |
3.78 |
2.89 |
0.21 |
0.009 |
0.001 |
Protein |
3.55 |
3.54 |
3.14 |
3.15 |
0.21 |
0.074 |
0.999 |
Lactose |
4.47 |
4.46 |
4.31 |
4.29 |
0.06 |
0.064 |
0.886 |
Blood measurements |
|
|
|||||
Urea, mg/dL |
25.7 |
23.9 |
18.4 |
18.1 |
1.54 |
0.007 |
0.628 |
Glucose, mg/dL |
56.1 |
61.7 |
56.1 |
57.6 |
1.28 |
0.120 |
0.012 |
Insulin, µg/L |
1.14 |
1.54 |
1.03 |
1.43 |
0.23 |
0.637 |
0.091 |
Lactate, mmol/L |
0.51 |
0.52 |
0.46 |
0.51 |
0.04 |
0.488 |
0.446 |
NEFA, mmol/L |
0.10 |
0.06 |
0.07 |
0.03 |
0.02 |
0.116 |
0.021 |
β-hydroxybutyrate, mmol/L |
0.65 |
0.48 |
0.77 |
0.48 |
0.07 |
0.369 |
0.002 |
1Effect of ambient temperature
23.5% fat-corrected milk = L of milk yield × [0.432 + 0.162 × (fat %)].
Keywords: heat stress, propylene glycol, dairy goats