Effects of limiting frequency of free access to milk on growth and intake of holstein calves during pre-and early post-weaning period

New born (male and female) calves (n = 26) weighing 33.3 ± 0.71 kg were used to evaluate effects of restricting frequency of free access to milk before and 2 weeks after weaning. Calves were randomly assigned at birth to 1 of 2 treatments being free access to whole milk twice daily (2X) or free access to whole milk once a day (1X). Milk and starter intakes were recorded daily, body weight (BW) was recorded weekly and metabolisable energy intake estimated. Before weaning, 2X calves had greater milk intake (8.76 L/d) and lower starter intake dry matter intake (DMI); 0.11 kg DM/d) compared to 1X calves (7.11 L/d and 0.21 kg DM/d, respectively; P < 0.01). Pre–weaning body weight (54.21 kg) and BW gain average daily gain (ADG) 0.74 kg/d were greater (P < 0.01) for 2X calves compared to 1X (45.30 kg and 0.58 kg/d, respectively). Feed and energy conversion ratio did not differ (P > 0.05) between treatments before weaning, but were greater (P < 0.03) in 1X calves compared to 2X calves after weaning. Calves fed 2X lost weight a week after weaning, while calves fed 1X maintained growth. Limiting frequency of free access to milk improved solid feed intake and helped calves maintaining apparent growth after weaning.


INTRODUCTION
The amount of milk consumed by young dairy calves influences gut development (Anderson et al., 1982) and determines intake of starter feed as well as their health and growth (Appleby et al., 2001).In conventional calfrearing systems, the amount of milk or milk replacer is limited to 8 to 10% of body weight (BW) during the first few weeks of life (Drackley, 2005) in order to encourage solid dry matter (DM) intake and allow early weaning.Studies to improve milk feeding systems for dairy calves through ad libitum milk feeding have shown higher milk consumption and BW gain, with reduced starter intake, compared to restricted milk feeding (Appleby et al., 2001;Hammon et al., 2002;Jasper and Weary, 2002).Delayed solid feed intake because of ad libitum milk consumption during the pre-weaning period (Appleby et al., 2001;Hammon et al., 2002) results in delayed ruminal development which is associated with poor post-weaning performance (Baldwin et al., 2004).Restricted milk feeding as well as reduced starter intake due to ad libitum milk feeding, lead to poor growth and welfare (Khan et al., 2007).Alternative milk feeding approaches for better performance and welfare of dairy calves are needed.Khan et al. (2007) reported that step-down milk feeding may prevent the problems of depressed solid feed intake associated with ad libitum milk feeding and of low BW gain with conventional milk feeding of dairy calves.A review of feeding systems (Khan et al., 2011) revealed that low milk feeding regimens (4 L/d) leaves calves hungry thereby compromising growth, health, welfare and future milk yield, but that higher milk allocation reduces feed consumption thereby increasing growth check in the days after weaning, suggesting that the optimal milk feeding strategy occurs between conventional and ad libitum intake.Khan et al. (2011) suggested that effects of solid feed level should be evaluated on calves fed higher amounts of milk.The hypothesis of the current study was that limiting free access to milk would keep high level of milk intake and increase intake of solid feed.Therefore the objective was to compare effects of free access to milk fed twice daily and free access to milk fed once daily on solid feed consumption, metabolisable energy (ME) intake, BW gain, and feed efficiency in Holstein calves during the pre-weaning and early post-weaning periods.

MATERIALS AND METHODS
The experimental protocol and procedures were approved by the Animal Ethics Committee (APIEC11/028) of the Agricultural Research Council at Irene (Pretoria) South Africa.

Animals and treatments
Twenty six holstein female (n = 16) and male (n = 10) calves averaging 33.3 ± 0.71 kg of BW at birth were used.Calves were born between between September 2012 and December 2013, at at the Agricultural Research Council Institute (S: 28013' 0" and E: 250 55' 0", altitude 1523 m) in South Africa.Calves were raised in individual calf pens until 70 d of age in an open front shed housing unit, with an exercise yard and proper floor rubber mats.Calves were blocked by birth date and randomly allocated to one of 2 experimental groups being: Free access to whole milk twice a day (2X) or free access to whole milk once a day (1X).All calves were fed colostrum for 3 d after birth.From day 4, calves fed 2X had free access to whole milk at 0800 and 1400 h, while calves fed 1X had free access to milk only at 0800 h.Milk was offered in 5 L buckets.The bucket was immediately refilled when empty until the calves stop drinking, and removed 30 min after to ensure cessation of drinking.From day 52, all calves were fed 4 L once a day at 0800 h until weaning at 56 days, when it was stopped completely.Fresh water and starter pellet (88.5 % dry matter (DM), 18.0 % crude protein (CP)) were available ad libitum from day 4 to 70.Average DM content of whole milk was 12.3 %, which contained 26.7 % fat, 28.2 % protein, and 34.2 % lactose.

Intake and measurements
Daily individual calf starter intakes were measured throughout the experiment, milk and water consumption by each calf was measured daily.Calf starter was sampled and analyzed for DM by oven drying at 60°C for 48 h and CP according to AOAC (2000) procedure 968.06.Composite daily milk samples from milk collected in the morning and evening were collected monthly to determine fat, CP, and lactose at lacto lab (Pty) (Irene) using a system 4000 infrared analyser (Foss Electric, Hillerod, Danemark).Calves were weighed at birth and at 7 day intervals throughout the experiment.Average body weight (BW) gain, total dry matter intake (DMI), feed conversion ratio (kg BW gain/kg of total DMI) and metabolisable energy (ME) conversion ratio (kg BW gain/kg of total ME intake) were calculated.Metabolisable energy concentration of whole milk was calculated according to NRC (2001).Faecal scoring to determine faecal fluidity and consistency occurred daily at 0800 h with the score ranging from 1 to 4, with '1' indicating formed stools, '2' when soft or of moderate consistency, '3' when runny or mild diarrhoea, and '4' when watery and profuse diarrhoea.At weaning, calves in both groups continued on the starter feed and remained in individual pens until 70 d of age when the experiment ended.

Statistical analysis
Data were analyzed for two periods (pre-and post-weaning) using a mixed-effects analysis of variance in SAS ( 2009) with frequency of access to milk and its interaction with time as fixed effects, and calf as random effect.Data were analyzed as average and repeated measures.Initial BW for the pre-weaning data, and BW at weaning for the post-weaning data, was both included in the model as covariates.Tukey's test (Samuels, 1989) was used for testing differences in Least Squares Means.Significance was declared at P < 0.05 and tendency to differ were accepted if P < 0.10 but > 0.05.

RESULTS
Milk intake (L/d, % BW and kg of DM/d) was greater (P < 0.05) and starter DMI (kg/d and % BW) was lower (P < 0.05) in calves fed 2X compared to calves fed 1X (Table 1).Total DMI and ME intake did not differ between treatments averaging 1.13 kg/d and 23.5 MJ/d, respectively.As expected, there was a week effect (P < 0.01) on intake.As calves aged, starter and milk intake increased.Average BW, BW gain and average daily gain (ADG) were greater (P < 0.01) for the 2X treatment compared to 1X, but BW gain as % of initial BW did not differ.Starter DMI as % BW was greater (P < 0.05) in calves fed 1X.There was a week effect (P < 0.001) on BW and DM intake as % BW.Feed conversion ratio and energy conversion ratio (ECR) were similar in both treatments.Post-weaning starter DMI (kg/d and % BW) and ME intake (MJ/d) did not differ between treatments and averaged 1.47 kg/d and 19.5 MJ/d respectively (Table 2).Body weight tended (P < 0.10) to be greater for 2X calves, while BW gain (kg), ADG, feed conversion ratio (FCR) and energy conversion ratio (ECR) were lower (P < 0.05) in the same group of calves.
The patterns of starter DMI and Milk intake are presented in Figures 1 and 2 respectively, and after 70 d, the general trend was still for the DMI to increase.In both treatments, starter DMI spiked from day 49 to 70.The spike was related to milk withdrawal.Starter DMI, g/kg BW remained higher (P < 0.05) for 1X calves before weaning (Table 1) and only numerically greater after weaning (Table 2).Figure 3 illustrates the growth curves of calves on 2 and 1X through 70 days of age.Higher BW's occurred for 2X calves until weaning (75.5 vs 64.9 kg for 2 and 1X; respectively).Calves in treatment 2X had a decline on BW during the first week after weaning    but recovered during the following week.Body weight gain for 1X calves was not affected during the transition to a solid diet.Results on faecal scores during the preweaning period are presented in Table 3. Faecal score did not differ (P > 0.05) between 2 and 1X averaging 2.16.Differences in faecal scores were observed only during weeks 3, 4 and 5, when it was higher for 1X calves compared to calves 2X calves.

DISCUSSION
Consistent with previous reports (Borderas et al., 2009;Appleby et al., 2001;Jasper and Weary, 2002;Khan et al., 2007), all calves increased milk consumption during the first 2 weeks, and consumed high amounts without noticeable increase in diarrhoea as observed previously.
Calves fed 2X consumed more milk, with intake level comparable to previously reported levels (Jasper and Weary, 2002;Moallem et al., 2010;Borderas et al., 2009) for calves fed milk ad libitum.Calves fed 1X consumed 18.8% less milk and doubled starter than 2X calves.This greater starter intake can be attributed to the hyperphagic response resulting from the reduction in milk availability by limiting free access (Khan et al., (2007).Early studies indicated that limiting milk intake encourages intake of calf starter (Maynard and Norris, 1923), and that rumen papillae growth is stimulated by VFA production, in particular butyrate, which is high in calves consuming large amount of starter (Tamate et al., 1962).Hence calves are often fed reduced volumes of milk with the aim of increasing starter DM intake, promoting rumen development and reducing the age of weaning.However, restricting milk affects calf welfare since calves naturally drink milk several times during the day.However, in our study calves fed 1X consumed much greater volume of milk (7.11 L/d) than conventional milk feeding (Jasper and Weary, 2002;Borderas et al., 2009), respectively 4.6 and 3.8 L/d) and improved starter DMI throughout the pre-weaning period.The total amount of starter DMI of 1X-fed calves (0.20 kg/d) was also much greater than the 0.17 kg/d (as fed) for calves fed milk conventionally (Jasper and Weary, 2002).In the latter study, milk weight totalled 0.1 g/kg of the calf's BW and was distributed evenly between two feedings.The difference on starter and milk intake between the two groups of calves did not entail differences in total DM and ME intake.Greater amounts of milk by 2X calves resulted in increased ADG during the milk feeding period, and despite higher pre-weaning started DMI, calves fed milk 1X gained 20% less BW than those fed 2X, probably due to a decrease in milk intake and associated decrease in nutrients availability.Calves fed 2X had BW (75.5 kg) at weaning (56 d) being comparable to Moallem et al. (2010) at weaning (60 d) for calves fed ad libitum whole milk (82.7 kg) and milk replacer (85.6 kg).Because total DM intake and ME intake before weaning did not differ between treatments, it is not surprising that there was no difference in FCR and ECR.
There was no differences in starter intake after weaning, suggesting that the difference in milk intake prior to weaning did not affect starter intake 2 weeks after weaning.Factors regulating intake and feeding frequency should be evaluated to help understanding the interaction of the amount and composition of nutrients from milk on solid feed intake.In contrast, Terre et al. (2007) and Weary et al. (2008) reported that high milk intakes before weaning can depress solid feed intakes after weaning if milk feeding is ended abruptly.In our study, the amount of milk was reduced to 4 L in the morning from d 52 to 56.
Calves fed 2X did not maintain their growth advantage after weaning.Their low post-weaning ADG may be attributed to reduced DM digestibility related to low DM intake of starter before weaning (Terre et al., 2007 andHill et al., 2010).It is also possible that increased DMI in 2X-calves after weaning has resulted in part of increased nutrient intake filling the gut rather than improving growth.
The earlier adaptation to high feed intake cushioned calves on 1X free access to milk from transitional effects of milk removal.Khan et al. (2007) indicated that earlier initiation of solid feed consumption and, possible, related ruminal activity can mitigate negative effects of ad libitum milk intake on pre-weaning and post-weaning feed intake, growth and performance of dairy calves.Although DMI per kg BW was higher for 1X calves through the entire experimental period, its effects on increasing BW gain only occurred after weaning.

Conclusion
Results suggest that high level of milk intake, similar to ad libitum milk feeding, and starter intake, similar to conventional milk feeding; can be attained when offering calves free access to milk only in the morning with ad libitum starter feed available all day.Body weight and feed efficiency post-weaning are comparable to unrestricted calves.However, further research is warranted to document long term effects of higher milk feeding frequency on performance of heifers, and in their first lactation.

Table 1 .
effects of frequency of free access to milk on intake, growth and efficiency (Least square means).

Table 2 .
Post-weaning (14 days) effects of frequency of free access to milk on intake, growth and efficiency (Least squares means).
Means in the same row differ if P<0.05; 2X: free access to milk twice (0800 and 1400 h) (14 days); 1X: free access to milk once a day (0800 h) (14 days); FCR: Feed conversion ratio; ECR: Energy conversion ratio.