Manure and Nutrient Accretion, Partitioning, and Excretion in Holstein Heifers
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Considerable changes have occurred in environmental regulations in recent years, only one of which is the requirement of stand alone heifer operations and feedlots to carry environmental permits. While growth of heifers is a widely researched topic, publications concerning nutrient utilization, partitioning, and excretion are scarce and are becoming necessary. That combined with the fact that feeding programs for heifers are highly variable from region to region and even from farm to farm indicated the need to examine the effects of diet on nutrient utilization. Therefore, the objective of this work was to evaluate how differences in levels of dietary protein and energy will affect growth and nutrient utilization in heifers from birth to calving. Two projects were conducted, one in 20 month old bred heifers where forage level in the diet was altered to provide the required nutrients in less feed and one in young calves where energy and protein content of the milk replacer was altered. Three diets were fed to 18 (n=6), 20 month old heifers who were in late gestation; the first was the high forage (HF) ration which was 90.7% forage and 9.3% concentrate, the second was a by-product (BP) ration which was designed to have the same level of fiber as the HF ration, however soybean hulls and cottonseed hulls were added at the sacrifice of the grain mix which increased the fiber content; the last ration was the low forage (LF) which was 54.7% concentrate and 45.3% forage and was fed at ~89% of the ad libitum intake of heifers fed the HF ration. Heifers fed the HF ration had greater fecal excretion compared to those fed LF, however heifers fed the LF ration exceeded the heifers fed HF and BP by 4.5 and 2.5 times, respectively, in urine volume excretion (40.2 vs. 8.9 and 16.9 kg/d, respectively). Although total N excretion (kg/d) was not different, heifers fed the LF ration tended to partition more N to urine than to feces. Phosphorus excretion in the feces was not different, however heifers fed HF and BP tended to have greater fecal P (P < 0.06). Urinary P excretion was less in heifers fed HF and BP compared to LF, however these heifers were excreting as much urinary P as a lactating cow.
Calves were purchased from a commercial dairy at 3 d old (± 1d) and transported to the VT Dairy Center. They remained on study until 63 d when they were harvested for body composition. Four treatment diets were fed; a control milk replacer (24/17; 24% CP, 17% Fat), a high protein, low fat (32/17; 32% CP, 17% Fat), a high protein, high fat (31/24, 31% CP, 24% fat), and that same 31/24 milk replacer fed at 1460 g/d powder (31/24+). Calves were offered a 20% cottonseed hull starter at 1 d after arrival to the VT Dairy Center. Calves fed 24/17 consumed more starter than those fed the other milk replacers and therefore had a lower apparent digestibility and greater fecal excretion. Fecal N excretion was not different, although calves fed 24/17 tended to have greater fecal N excretion. Urinary N excretion was higher in calves fed 31/24+ compared to those fed 31/24. Total N excretion and N retention were not different. Empty body weight (EBW) gain was greater in calves fed 31/24+ compared to 31/24, however those same calves also had a higher percent of EBW as fat. Calves fed 32/17 had the most lean gain (in the form of N gain) compared to those fed extra energy (31/24) and also had a higher N as a percent of EBW.
Limit feeding Holstein heifers late in gestation did not reduce nutrient excretion, however, more digestible nutrients were available to the heifer and fetus. Heifers in late gestation are likely over fed P and therefore excrete nearly everything they consume which has negative implications for nutrient management planning. Calves fed a low protein, low fat milk replacer did not grow as well as calves fed higher protein. Nitrogen retention and CP gain were higher when protein was at least 31% and fat was at least 17%. Feeding fat over 17% only increased fat gain and not CP gain. Overall, paying for extra nutrients in bred heifer diets seemed to be beneficial, however, feeding above 31% CP and 17% fat increased nutrient loss to the environment.
- Doctoral Dissertations