Reducing the length of time spent grazing pastures has been proposed as a strategy to reduce the amount of nitrogen (N) that is deposited on pasture. (For example, our duration controlled grazing summary).
Cows can compensate by eating more herbage over this shorter grazing period in order to maintain their dry matter intakes, however, the efficiency in which the feed is digested in the rumen can be reduced.
Adding supplementary feed is an obvious solution to maintain DM intakes and digestion efficiency, while reducing the time spent grazing. But is the timing of when the supplement is fed in relation to the grazing period important?
Key Points:
Cows that were fed maize silage 9 hours before their herbage, ate more herbage per day than the cows that were fed maize silage 1 hour before their herbage.
Milk yield was greater for cows fed maize silage 9 hours before herbage than the cows fed 1 hour before herbage.
There were no observed differences in the amount of N that was partitioned into the milk, faeces or urine between the 2 groups.
Keywords: #milkproduction #dairynutrition #maizesilage
This study was conducted at the Lincoln University Research Dairy Farm in the summer of 2012.
10 lactating FxJ cows that were rumen fistulated were used (5 in each treatment group).
Treatment 1: ~5 kgDM per cow of maize silage fed 1 hour before their herbage meal (after the afternoon milking).
Treatment 2: ~5 kgDM per cow of maize silage fed 9 hours before their herbage meal (after the morning milking).
All cows were offered 11 kgDM of freshly cut herbage (perennial ryegrass and white clover) over the 4 hours from 4pm until 8pm.
Cows were maintained on a stand-off area when not being milked or fed. This way the researchers were able to closely monitor each cow’s feed intake. Cows were adapted to these new diets for 9 days, followed by 5 days of measurements.
The metabolisable energy (ME) of the herbage fed was 11.7 MJ and ME of maize silage fed was 9.7 MJ.
Does the timing of feeding maize silage have an impact on herbage intake?
Maize silage intake was not different between cows fed maize silage 1 hour or 9 hours before herbage feeding.
Cows that were fed maize silage 9 hours before herbage, ate more herbage per day than the cows that were fed maize silage 1 hour before herbage. This is likely due to “rumen fill constraints” of being fed maize silage in such a short time before the herbage feeding.
In a management system where cows are allocated less time grazing or one grazing event in the afternoon, feeding supplements after the morning milking instead of after the afternoon milking may allow for greater pasture consumed and hence a greater total daily DM intake.
Does the timing of feeding maize silage have an impact on milk production?
As a result of the greater DM intake, milk yield was greater for cows fed maize silage 9 hours before herbage than the cows fed 1 hour before herbage (18.8 vs 15.4 kg milk/day).
Numerically, milk solids appeared to be greater for cows fed maize silage 9 hours before herbage than the cows fed 1 hour before herbage, but were not statistically different between the 2 treatments (1.63 vs 1.48 kg/day; P=0.08).
Remembering that this study was only conducted for 14 days total (including the adaptation period to the new diets), with only 5 cows per treatment, perhaps a longer study with more cows may have more consistent differences in milk composition (i.e. fat and protein percentage differences).
The authors of this study suggested that a longer experiment should be conducted to get into the longer term effects of the timing of maize silage supplementation on milk composition in cows that were restricted in herbage.
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Does the timing of feeding maize silage have an impact on nitrogen?
In this study, there were no observed differences in the amount of N that was partitioned into the milk, faeces or urine between the 2 treatment groups.
What this means is that the timing of feeding maize silage relative to herbage did not result in more N being moved (or partitioned) into one area (e.g. milk) compared to another (e.g. faeces).
Rumen “digesta” (digested feed sampled out of the rumen) were collected at 10 time points over a 24 hour time period.
One thing that was measured in the rumen sample was the concentration of ammonia (or NH3). After each feeding event, there was an increase in the concentration of NH3 in the rumen. As can be seen in Figure 2, the cows that were fed maize silage 9 hours before their herbage feed had 2 spikes in NH3 concentration, whereas the cows that were fed maize silage only 1 hour before their herbage feed only had one spike of NH3.
The peak of this spike was 27% higher for the cows fed maize silage 1 hour before than for the cows fed maize 9 hours before herbage.
The authors suggested that for the cows fed maize silage 9 hours before their herbage feed, their rumen microbes may have been better able to utilise NH3 and therefore capture N and have greater microbial growth during the herbage feeding session compared with the cows fed maize silage only 1 hour before their herbage meal.
Microbial growth was not directly measured in this study, however, the ratio of purine derivatives to creatine in urine was measured as an indicator of microbial growth. Cows that were fed maize silage 9 hours before herbage had greater ratios of purine derivatives to creatine than cows fed 1 hour before herbage.
Given that urinary creatinine is directly related to body mass and is excreted at a constant rate, the ratio of purine derivatives (microbial activity) to the constant creatine can be used to compare microbial growth between the 2 treatments.
The greater ratio for the 9 hour fed cows suggest a greater microbial protein production for this group compared with the 1 hour treatment group.
So, was the timing of feeding maize silage important?
In this study, where cows were fed restricted herbage in the evening, supplementing with maize silage after the morning milking (9 hours before herbage) increased DM intake and milk yield compared with feeding maize silage after the afternoon milking (1 hour before herbage).
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