| North Dakota
Agricultural Research North Dakota State University, Fargo, ND 58105
Feeding Value of
Field Pea and Hull-less Oat in Growing Calf Diets (continued) |
Abstract |
 DiscussionIn terms of cattle performance, these data suggest that pea and hull-less oat are suitable substitutes for barley and SBM when concentrate replacement is on an equivalent protein basis and fed in backgrounding type diets. Average daily gains were not affected by the inclusion of either of the test grains. Other studies have also reported similar ADG when hull-less oat replaced barley in growing calf diets (Johnson et al., 1995; Anderson et al., 1997). Poland and Faller (1997) and Schimek et al. (1997) reported linear decreases in ADG when hull-less oat was included in lamb (barley control) and steer (corn control) finishing diets, respectively. Johnson et al. (1995) and Anderson et al. (1997) reported increases in ADG when hull-less oat replaced barley in cattle diets. Many of these differences between control and hull-less oat containing diets in ADG seem to be related to changes in DMI, type of grain processing and/or base grain in the control diet. Johnson et al. (1995) reported no differences in DMI when hull-less oat was included in backgrounding calf diets and compared to coarsely ground barley. An increase in ADG was only observed in one experiment where oat was also coarsely ground. When whole hull-less oat was fed, no differences in DMI or ADG were observed. Other studies have reported decreases in DMI when diets contained various levels of hull-less oat (Poland and Faller, 1997; Schimek et al., 1997). Intake and ADG were closely correlated when whole hull-less oat was compared to whole barley in growing lambs (Poland and Faller, 1997) and when ground hull-less oat was compared to ground corn in finishing cattle (Schimek et al., 1997). Only one study (Anderson et al., 1997) documented a decrease in DMI with a corresponding increase in ADG. In this study, dry-rolled hull-less oat was compared to dry-rolled barley. The disparity between DMI and gain occurred during a fnishing phase (last 103 days of 181 days on feed). During a grower phase (0-78 days), DMI was decreased while ADG was unaffected by level of hull-less oat in the diet. Dry matter intake was also decreased with the inclusion of hull-less oat in the present experiments with no change in ADG. Bauer (1997) suggested that a decrease in intake can be expected when diets containing hull-less oat are compared with diets containing barley or corn. Three factors were cited as possibly contributing to this phenomenon. These included ruminal acidosis, dietary fat level and protein degradation or supply. Whether any or all of these factors contributed to the reduced intakes of hull-less oat containing diets in these experiments is unclear. When diets are low in roughage or where roughages are finely ground, acidosis can occur (Fahey and Berger, 1988). The oat hay used in both of these experiments was ground using a 2 in screen prior to mixing in diets. Although hay particle size was not measured, visual observations did not suggest that forage particle size would create an acidotic problem. Fat supplementation above 6% of diet dry matter can reduce digestibility of other feed ingredients in the rumen, which may in turn lead to a decrease in dry matter intake (Bauer, 1997). However, the total fat concentration of diets fed (Tables 2 and 3) in these experiments did not exceed 6%. Deficiencies of ruminally-available protein (DIP) and metabolizable protein supply (MP) were also implicated as possibly producing a reduction in dry matter intake in hull-less oat containing diets (Bauer, 1997). An evaluation (Bauer, 1997) of hull-less oat containing diets using a nutrient requirment model (NRC, 1996) to assess the adequacy of DIP and MP supply did not indicate that either of these were consistently related to depressions in dry matter intake in the diets used in these experiments. Similar ADG and decreased DMI resulted in improved FE when hull-less oat replaced barley. Improvements in FE with the inclusion of hull-less oat in barley-based diets have been previous reported (Johnson et al., 1995; Anderson et al., 1997). Feed efficiency did not differ when barley was replaced by whole (unprocessed) hull-less oat (Johnson et al., 1995; Poland and Faller, 1997) or when corn was replaced by ground hull-less oat (Schimek et al., 1997). Improved FE associated with diets containing processed hull-less oat suggest their net energy concentrations exceed those containing barley and SBM (NRC, 1984). A separate explanation for the improved feed efficiencies of hull-less oat containing diets relates to a negative relationship between level of intake and digestibility (Merchen, 1988) or efficiency of nutrient use (Merchen and Bourquin, 1994). Intake effects on diet digestibility are much more pronounced with mixed diets than with diets consisting of single feedstuffs (Merchen, 1988). In mixed diets, decreases of approximately 4% for each unit increase in DMI have been reported. A unit of intake (MM) equals level of DMI necessary to achieve zero energy balance or maintenace. Depressions in digestibility due to increasing DMI are thought to result from increased rate of passage of digesta through the digestive tract (Merchen, 1988). However, the depression in digestibility due to increased intake may not be of major importance in a growing-finishing animal in which DMI rarely exceeds 3 MM, but can become quite meaningful in a lactating dairy cow where DMI may exceed 5 MM (Ferrell, 1988). Generally, in diets of sufficient quality and consumed at approximately 3 MM, a correction of metabolizable energy concentratioin due to feeding level is not necessary (Ferrell, 1988). Dry matter intake of calves consuming control diets (Tables 4 and 5) equated to 2.75 and 3.09 MM for experiments 1 and 2, respectively. Average depressions in DMI between the hull-less oat and control diets were 1.7 (.27 MM) and 3.9 (.48 MM) lb for experiments 1 and 2, respectively. Although an effect of DMI on diet digestibility was not determined in these experiments, the changes in DMI were not seen to be large enough to account for the observed improvements in FE for diets containing hull-less oat. Average NEm and NEg values for
hull-less oat grain were 1.17 and .84 Mcal/lb,
respectively (see Table 6). If these values are
adjusted for experimental bias and fat
concentration (Table 7), the net energy
concentration of hull-less oat is similar to oat
groat and numerically greater than corn (NRC,
1984). Until additional data is collected,
assuming that the net energy concentration of
hull-less oat equals that of oat groat seems
reasonable. Thus, conservative estimates of the
NEm and NEg value of hull-less oat in growing
calf diets are 1.07 and .75, respectively. When
NE concentration of test grains in Exp 2 were
assumed, the NE concentration of COMB2 (.78 and
.51 Mcal/lb for NEm and NEg, respectively) was
calculated to be similar to the dietary NE of
FPEA2 (.78 and .50) and HOAT2 (.78 and .51). This
similarity was expected given the relative
similarity of the estimated NE concentration of
FPEA2, HOAT2 and COMB2 (Table 6).
The protein in pea is highly degradable in the rumen (DIP, 78% of CP; Hickling, 1994). Thus, pea protein may be an excellent supplemental source of DIP at times when a base diet is determined to be deficient in ruminally-available nitrogen. In South Dakota (C. Birkelo, personal communication), pea improved FE in finishing cattle consuming a high-concentrate, corn grain based diet. Corn grain is relatively high in energy, low in CP (relative to energy) and low in DIP (NRC, 1996). Pea may have alleviated an inherent DIP deficiency in the base diet, allowing for an overall improvement in diet digestibility. Personal observations using a nutrient requirement for beef cattle (NRC, 1996) suggests that forage-based diets are typically first-limiting in DIP. Whether DIP supply from pea containing diets can explain the enhancement in FE seen in Exp 2 is speculative. Nonetheless, given the abundance of forage produced in northern Great Plains, this possibility needs further study.
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