Influence of suckling before milking on yield and composition of milk from dual purpose cows with restricted suckling

The experiment was carried out in Maracay, Venezuela, with 24 Brahman X Holstein cows of two or more parities and a proportion of 5/8 to 3/4 Holstein. The cows grazed on Cynodon nlemfuensis, Brachiaria mutica and Digitaria swazilandensis all day, except during machine milking that started at 06:30 and 16:00 h. They received 2.5 kg/day of concentrate at each milking, prepared on the farm with 48 % extracted maize germ, 48 % wheat middling, 2 % salt and 2 % mineral mixture.

The calves were housed in partially roofed individual pens (2 x 6 m) with a concrete floor, where water, chopped forage and the concentrate described for the cows were offered ad libitum, except during the first three days after calving when they were kept with their dams. For the treatments with restricted suckling before milking, the calves were taken to the milking parlor, located some 30 m from their pens, and were allowed to suck all four teats for approximately 1 minute, until “let-down” was observed. Immediately afterwards, they were separated from their dams and returned to their pens, while milking continued. At the end of the morning milking, all cows were taken to the calf housing area and allowed to suckle their respective calves in their individual pens for approximately 30 minutes, after which they were returned to the field for grazing. After the afternoon milking, restricted suckling before milking was practiced only in the “AM+PM” treatment, after which all cows were returned to the field for grazing. The calves were weaned when they reached 90 kg liveweight.

The cows were weighed weekly after calving and saleable milk was measured daily at each milking. A weekly sample of morning and afternoon saleable milk was taken for fat analysis, from a bucket where all milk from the machine milking bottle was transferred and thoroughly mixed. Milk consumed by the calves was estimated weekly, weighing them before and after suckling.  A milk sample was taken just after suckling started. Fat content of saleable and consumed milk samples was determined by the Babcock method (AOAC 1984). Intake of forage and concentrate by the calves was measured once a week and samples were taken for later analysis for crude protein (AOAC 1984) and neutral detergent fiber (Goering and Van Soest 1970).

The liveweight gain of the calves was estimated by linear regression of the weekly weights on time. Saleable, consumed and total milk yields were corrected by milk yield during the previous lactation and adjusted means were calculated. Means of variables analysed were compared with Duncan’s multiple range test (SAS 1996).

Total milk yields before weaning were similar in the three treatments (Table 1), but the components of total yield were influenced by restricted suckling before milking. Milk consumption by the calves decreased (P<0.05) from 2.9 kg/day without restricted suckling before milking to 1.7 kg/day when restricted suckling before milking was applied at the twice daily milking. The opposite occurred with saleable milk, which increased (P<0.05) from 7.0 kg/day without restricted suckling before milking (treatment W)  to 8.9 and 8.1 kg/day in treatments AM and AM+PM. The percentage of total milk consumed by the calf was appreciably reduced with restricted suckling before milking and was almost halved between treatments W and AM+PM (30 vs. 17 %). Liveweight losses of the cows (from just after calving until week 14, when all cows were still suckling their offspring) were very similar, varying between 19 and 21 kg (Table 1). 



Milk fat content was influenced by restricted suckling beforemilking. Fat in consumed milk increased from 6.0 to 7.4 % between treatmentsW and AM (P<0.10) and the same trend was observed in morning saleable milk,increasing from 2.1 to 2.6 % in treatments W and AM+PM (P<0.10). Correctingmilk yields to 4 % fat (FCM), appreciably raised milk consumption values andreduced saleable milk, with consequent effect on the components of total milkyield (Table 2), but the influence of treatments on these components followedthe same trend observed with milk uncorrected for fat content.

Liveweights of the calves at birth, at weaning and 30 days after weaning were similar for all treatments (Table 3). The time to reach weaning weight varied between 124 and 131 days. Intake of concentrate (21.9 % crude protein and 46.2 % NDF) and forage (6.8 % crude protein and 78.1 % NDF) from birth to weaning did not vary between treatments. 

The main effect of restricted suckling before milking was a change in the components of milk yield, without major changes in the total quantity of milk. The proportion of saleable milk increased, at the expense of milk consumed, and its fat content also increased (Table 1). These results are of practical importance to the farmer, because more milk with a higher content of fat is available for sale, without negative effects on calf growth rate. The cause of the larger amounts of saleable milk induced by restricted suckling before milking cannot be explained with the information available. Bar Peled et al (1995) observed higher levels of blood oxytocin (OT) with suckling than with machine milking, when they were alternated every four hours, and this resulted in larger amounts of milk suckled than milked. Possibly larger OT peaks also occurred in the AM  and AM+PM treatments in this trial, resulting in a higher amount of alveolar milk ejected and removed by the machine. But milk was not completely removed in any of the treatments, because the amount of milk obtained by suckling  during the approximately one hour period following milking (1.7 to 2.9 kg) was always larger than the estimated milk yield per hour drawn by the machine, which was between 0.41 and 0.48 kg. Two factors, not evaluated here, could be related to the partial milk removal during milking following suckling before milking: the absence of elevated OT concentrations during the entire milking process (Bruckmaier and Blum 1996) and peripheral inhibition of OT effects (Bruckmaier et al 1997).

The higher fat content in consumed than in saleable milk has been reported by several authors (see review by Sandoval et al 1995) and could be explained by an irregular distribution of fat in the milk inside the udder, concentrated mainly at the top of the milk accumulated in the cistern. The higher fat content of saleable milk in AM and AM+PM treatments could also be related to the removal during milking of a proportion of the fatty milk that otherwise would have remained in the udder and sucked later by the calf. It also explains the higher fat concentrations in the smaller amount of suckled milk observed in these treatments, because the fat content of suckled milk increases with time  (Sandoval-Castro et al 1995).

Total milk was not influenced by suckling before milking (Table 1), but a trend for yield to be higher on treatment AM than in treatment W was observed after correcting it for fat (Table 2). Total milk yield was underestimated on treatments AM and AM+PM, because milk consumed during suckling before milking was not measured. More recent information (M. Tesorero, unpublished results), obtained from a treatment similar to AM+PM, has shown that the quantities taken by the calf during suckling before milking reach values of 0.73±0.20 and 0.51±0.14 kg in morning and afternoon milking, respectively.  These are significant amounts considering the relatively low milk yields obtained in dual purpose systems. If it is assumed that similar amounts were suckled before milking in this trial, total milk yields in treatments AM and AM+PM increase from 11.4 and 9.9 kg/day (Table 1) to 12.1 and 11.1 kg/day. These amounts would be 13 and 20% higher than the yield (9.8 kg/day) obtained without suckling before milking.  The implication is then that suckling before milking also increases total milk yield.

The proportion of the total FCM consumed by the calves (Table 2) reaches very high values if suckling before milking (W) is not practiced. However, the growth rates of the calves on the ‘W” treatment were no better than those that were suckled before milking (AM and AM+PM) (Table 3). Lower milk consumption is usually accompanied by higher solid feed intakes (Forbes 1995), but forage and concentrate intakes were similar in all treatments on this trial. As mentioned before, milk consumed did not include the milk suckled before milking and, even considering that it might have a significantly lower fat content than other milk fractions, it could partially compensate the lower milk consumption observed after milking in AM and AM+PM treatments and thus explain the absence of growth rate differences compared with treatment W.

The findings from this study have shown that stimulation of the udder by calf suckling before milking in dual purpose systems with restricted suckling after milking:

• Increases saleable milk and reduces the amount sucked milk after milking.
• Increases saleable fat content.
• Does not affect calf growth rate if a feed supplement is provided.

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