Ovarian follicular response to oestrous synchronisation and induction of ovulation in Norwegian Red cattle

Table 2 Survival analysis of time to ovulation following oestrous synchronisation

Variable	Level	Estimate^c	SE	Hazard ratio (e^b)
Herd	1	–	–	R
	2	0.14	0.12	1.15
	3	− 0.05	0.06	0.95
	4	0.04	0.06	1.04
Age	Heifers 14‒15 months	–	–	R
	Heifers 16‒18 months	− 0.10^a	0.05	0.90
	Heifers 19‒28 months	− 0.20^a	0.10	0.82
	Cows parity 1‒3	− 0.02	0.06	1.02
Initial follicle size^d	≤ 10.0 mm	0.05	0.04	1.05
Initial follicle size^d	> 10.0 mm	–	–	R
Diameter at ovulation^a,e	9.0‒15.0 mm	–	–	R
	15.1‒17.4 mm	− 0.15^b	0.05	0.86
	17.5‒23.0 mm	− 0.12^a	0.06	0.89
BCS	Lean (2.5‒2.9)	0.07	0.07	1.07
	Moderate (3.0‒3.4)	–	–	R
	Fat (3.5‒4.0)	0.08	0.05	1.08

Hazard ratio for time to ovulation by herd, and classes of age, initial follicle size, follicle diameter at ovulation, and body condition score (BCS) in Norwegian Red cattle; time variable: hours from GnRH analogue treatment to ovulation; R, reference value and SE, standard error
^aOverall association with time to ovulation or within variable difference relative to the reference value; P ≤ 0.05
^bWithin variable difference relative to the reference value; P < 0.001
^cEstimate for each parameter level
^dDiameter (mm) of the dominant follicle at the time of GnRH analogue treatment (T0)
^eDiameter (mm) of the dominant follicle at the time of ovulation

ISSN: 1751-0147