RISK FACTORS FOR HYPOCALCEMIA INCIDENCE AND THEIR EFFECT ON MILK YIELD AND REPRODUCTION IN A GRAZING JERSEY, GUERNSEY AND HOLSTEIN HERD IN COSTA RICA

Abstract Text:

The aim of this study was to determine risk factors for hypocalcemia (blood Ca concentration under 8.0 mg/dl) and its effect on milk yield and reproduction in three breeds of dairy cows under the same feeding, management and environmental conditions. The study was conducted on a dairy farm located in Cartago, Costa Rica and comprised a total of 152 cows (62 Jersey, 41 Guernsey and 49 Holstein). Average lactation number for the three breeds was 2.73±1.59. During the close up period cows grazed kikuyu grass (Kikuyuocloa clandestina)(14.8% DM, 23.4% CP, 54% NDF, 0.35% Ca, 0.31% Mg and 3.50% K) and were supplemented with 4 kg/animal/d of a concentrate mixture low in Ca (14% CP, 31% NDF, 0.2% Ca, 0.42% Mg and 1.38% K) and 1 kg of hay (82.3% DM, 5.1% CP, 61.4% NDF, 0.4% Ca, 0.35% Mg and 1.8% K)/ d. Cows were fed 1 kg of concentrate (18.6% CP, 0.90% Ca, 0.42% Mg and 1.38% K)/ 2.5 to 3.0 kg of milk during lactation. Blood samples of cows within 24h from calving were taken from the coccygeal vessels and analyzed for Ca, using atomic absorption spectrophotometry, to establish relationships with productive, reproductive and inherent variables. Results are shown in Table 1.

Table 1. Variables associated with blood Ca concentration in peripartum (calving ±1d) according to breed.
Variable	Ca concentration as association variable				Breed
	Pearson correlation		Linear regression
	Rho	P	R2	P
Previous milk yield **	-0.516	0.012	0.266	0.012	Guernsey
Actual milk yield*	-0.371	0.043	0.138	0.043	Guernsey
BCS at calving**	-0.312	0.024	0.097	0.024	Jersey
Calving number**	-0.335	0.008	0.112	0.008	Jersey
Calving number**	-0.323	0.024	0.085	0.024	Holstein
Calving interval*	-0.403	0.027	0.163	0.027	Holstein
* Ca dependent variable, ** Risk factor for hypocalcemia.

Milk yield in the previous lactation in Guernsey, BCS at calving in Jersey and calving number in Jersey and Holstein cows were risk factors (P<0.05) for suffering hypocalcemia at peripartum. Likewise, Ca concentration was related (P<0.05) to actual milk yield in the succeeding lactation in Guernsey, and to calving interval in Holstein. These results suggest that Ca concentration at parturition in Guernsey cows could be driven by productive variables and in Jersey and Holstein cows seems to be related to inherent factors. These variables should be studied in a wider population for a better understanding of the causes of hypocalcemia incidence in dairy cattle.

Keywords: Dairy cows, hypocalcemia, risk factors