Poor estrus expression is considered one of the main causes of declining fertility in dairy cows where artificial insemination is used. One of the factors that affects estrus expression is the body condition score (BCS). This study aimed to investigate the effect of BCS on the number of steps and lying time (h/d) during estrus. Lactating Holstein Friesian cows (n = 92) were used from 14 d postpartum with mobility score 2.1 ± 0.5 (mean ± SEM) and milk yield 31.6 ± 9.3 kg/d at the Harper Adams University dairy unit. Cows were housed in a free stall yard with sawdust covered, rubber mattresses, and grooved concrete passageways. They were fed a TMR ad libitum with grass during the summer. Their BCS was measured according to AHDB Dairy (2014). Milk samples were collected 3 d per week for progesterone (P4) ELISA (Ridgeway Science Ltd., UK). Activity was monitored continuously using IceQubes (IceRobotics Ltd., Edinburgh, UK) attached to the back left leg. A cow was considered in estrus when milk P4 concentration was <3 ng/mL, followed by an increase to >15 ng/mL and an IceQube estrus alert was recorded. The data were analyzed by repeated measures ANOVA (GenStat 17th edition). The number of steps were increased (Table 1) and lying times (h/d) were reduced (P < 0.001) on the day of estrus (0) compared with 3 d before and 3 d after estrus. On the day of estrus, more steps (P < 0.001) were recorded in BCS 2.75 cows compare with BCS ≤ 2.5 and BCS ≥ 3 cows. Lying time were higher (P < 0.001) in BCS ≤ 2.5 cows compared with other BCS. The interaction between BCS and time was significantly (P < 0.001) affected on lying time. In conclusion, dairy cows that had a BCS 2.75 during estrus spent more time active at the expense of the lying time on the day of estrus. Table 1. Mean number of steps per day and lying time (h/d) 3 days before, day of estrus (0) and 3 days after estrus and between BCS ≤2.5 (n = 22), BCS 2.75 (n = 81) and BCS ≥3 (n = 35)

Activity		BCS	Day							SED	P-value
−3	−2	−1	0	1+	2+	3+	BCS	Day	BCS× day
Steps, no./d		≤ 2.5	1472	1468	1756	3982	1768	1410	1392	227.3	0.288	<0.001	0.715
	2.75	1611	1522	1716	4481	1890	1705	1579
	≥3	1652	1686	1783	4362	1965	1718	1716
Lying time, h/d		≤ 2.5	11.8	12.3	12.0	10.0	12.1	12.0	12.3	0.547	<0.001	<0.001	<0.001
	2.75	10.2	10.1	9.6	6.1	11.0	10.8	10.4
	≥3	10.1	9.9	9.7	6.7	11.3	10.9	10.7