340 Relationship of Retained Energy in Lactating Beef Cows to Maintenance Energy Requirement and voluntary Feed Intake

This study’s objective was to determine the relationship between retained energy, lactation maintenance energy requirement (MER), and dry period voluntary feed intake (VOL) in beef cows. Twenty-four mature fall-calving Angus cows were used in an 82-d study during lactation to establish maintenance energy requirements followed by a voluntary feed intake study after weaning. During the lactation MER experiment, cows were housed in 2 drylot pens and limit-fed a mixed hay/concentrate diet (17.8% CP, 2.6 Mcal/kg ME, DM basis) individually once per d in a stall barn. Cows were adapted to the diet and feeding management for the first 16 d. Subsequently, cows were weighed and feed allowance adjusted at 14-d intervals to achieve BW and BCS stasis. Milk yield and composition were determined on d – 10, 49, and 77 using a milking machine. Retained energy was calculated as average daily maternal tissue energy change plus average daily milk energy yield. During the post-weaning VOL experiment, cows were provided ad libitum access to a grass hay diet for 41 d (8.15% CP, 1.8 Mcal/kg ME, DM basis) using five individual feed intake monitoring units (SmartFeed, C-Lock, Inc). Each one unit increase in metabolizable energy intake, kcal/kg BW0.75 was associated with a 0.86 ± 0.28 kcal/kg BW0.75 increase in total retained energy (P = 0.005). Using this partial efficiency coefficient, ME required for maintenance declined by 0.80 ± 0.11 kcal ME/kg BW0.75 for each additional kcal net energy retained/kg BW0.75 (P < 0.0001). There was no relationship between lactation-period retained energy and post-weaning VOL forage dry matter intake. The present study results contradict previous reports suggesting that maintenance requirements increase with increasing productivity.

PSXI-29 Effects of feed restriction on blood constituent concentrations in hair sheep

Forty-six Dorper, 47 Katahdin, and 41 St. Croix female sheep (initial body weight of 62, 62, and 51 kg, respectively, SEM=1.43; 3.8±0.18 yr of age) from 45 commercial farms in Midwest, Northwest, Southeast, and central Texas regions of the United States were used to evaluate effects of feed restriction on concentrations of blood constituents. A 50% concentrate pelleted diet was fed, with the amount varied in the first 4 wk to achieve stable BW. The amount of feed offered in wk 5–10 was set at 55% of that consumed in wk 3–4. Blood was sampled at the end of wk 3, 4, 6, 8, and 10, with constituent levels in wk 4 and 10 assumed relevant to conditions with different maintenance energy requirements (i.e., fed at maintenance and approximately 43% lower with restricted intake). There were some differences among breeds such as ones based on samples collected at all times in urea nitrogen (14.0, 13.7, and 15.4 mg/dl; SEM=0.31) and creatinine (0.945, 0.836, and 0.809 mg/dl for Dorper, Katahdin, and St. Croix, respectively; SEM=0.0253) but relatively few among regions and only one interaction between week and breed or region. There was a trend for a difference (P = 0.051) between wk 4 and 10 in the concentration of glucose (51.9 and 54.2 mg/dl; SEM=0.90), and there were differences (P < 0.05) in levels of lactate (23.9 and 20.3 mg/dl; SEM=0.89), urea N (16.4 and 13.0 mg/dl; SEM= 0.25), creatinine (0.808 and 0.919 mg/dl; SEM=0.0165), triglycerides (31.8 and 25.5 mg/dl; SEM=0.63), cholesterol (67.5 and 74.7 mg/dl; SEM=1.66), and cortisol (10.55 and 8.31 ng/ml for wk 4 and 10, respectively; SEM=0.0542). In conclusion, similar responses of different hair sheep breeds in blood constituent levels to feed restriction is in accordance with comparable effects on body weight and the maintenance energy requirement previously reported.

Heat processing increased the digestibility of phosphorus in soybean expeller, canola meal, and canola expeller fed to growing pigs

It is hypothesized that heat processing may increase P digestibility in different protein sources fed to growing pigs. A study was conducted to determine the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in soybean expeller (SBE) produced from oil extraction using dry extrusion and expelling and to investigate the effects of heat treatment on the ATTD and STTD of P in SBE, canola meal (CM), and canola expeller (CE) fed to growing pigs. Thirty-six growing barrows with an initial body weight of 19.0 ± 1.0 kg (mean ± SD) were assigned to 1 of 6 experimental diets in a completely randomized design to give 6 replicates per diet. The experimental design was a 3 × 2 factorial arrangement including three oilseed meals with or without heat treatment. The diets were formulated to contain non-autoclaved or autoclaved (at 121°C for 60 min) SBE, CM, and CE as the sole source of P. Limestone was included in diets to maintain a Ca:total P ratio of 1.3:1 across diets. Pigs were individually housed in metabolism crates for 12 days, including 7 days for adaptation and 5 days for total collection of feces. Pigs were offered their daily ration at 2.8 times their maintenance energy requirement. Data were analyzed using the PROC MIXED of SAS. Heat treatment increased (P < 0.05) the ATTD and STTD of P. Pigs fed the SBE diets had greater (P < 0.05) ATTD and STTD of P than pigs fed CM and CE diets. For the autoclaved ingredients, the values of STTD of P were 49.4, 23.2, and 25.8% for SBE, CM, and CE, respectively, whereas STTD of P in non-autoclaved SBE, CM, and CE were 48.5, 20.2, and 22.5%. Heat treatment increased (P < 0.05) the ATTD of Ca. In conclusion, heat treatment increased ATTD and STTD of P and ATTD of Ca in SBE, CM, and CE fed to growing pigs. The ATTD and STTD of P in SBE determined in the current study were 41.0 and 48.5%, respectively.

139 Digestibility of phosphorus in heat-treated dry extruded-expelled soybean meal and solvent-extracted and expeller-extracted canola meal fed to growing pigs

Although heat treatment affects digestibility of amino acids in feed ingredients, there is less information as to whether such an effect also applies to minerals. Therefore, the objective of this research was to investigate the effects of heat treatment on apparent (ATTD) and standardized total tract digestibility (STTD) of P in dry extruded-expelled soybean meal (DESBM), solvent-extracted canola meal (SCM), and expeller-extracted canola meal (ECM) fed to growing pigs. A total of 36 pigs (19.0 ± 1.0 kg) were assigned to 1 of 6 diets in a completely randomized design to give 6 replicates per diet. Pigs were individually housed in metabolism crates for 12 d, including 7 d for adaptation and 5 d for total collection of feces. The experimental diets were formulated to contain non-heated or heat-treated DESBM, SCM, and ECM as the sole source of P. Pigs were offered their daily ration at 2.8 times their maintenance energy requirement. Data were analyzed as a 3 × 2 factorial arrangement using the PROC MIXED of SAS with ingredients, heat treatment, and their interaction; however, no interaction was observed for any variable. Pigs fed the DESBM diet had a higher (P < 0.05) ATTD and STTD of P than pigs fed SCM and ECM diets. The ATTD and STTD of P in heat treated samples were higher (P < 0.05) than in non-heated samples. In the heat-treated samples, the values of STTD of P were 49.4, 23.2, and 25.8% for DESBM, SCM, and ECM, respectively. Respective values for STTD of P in non-heated DESBM, SCM, and ECM were 48.5, 20.2, and 22.5%. The ATTD of Ca in non-heat-treated samples was lower (P < 0.05) compared to the values for heat-treated samples. In conclusion, heat treatment increased ATTD and STTD of P in DESBM, SCM, and ECM fed to growing pigs.

Severe below-maintenance feed intake increases methane yield from enteric fermentation in cattle

The relationship between feed intake at production levels and enteric CH4 production in ruminants consuming forage-based diets is well described and considered to be strongly linear. Unlike temperate grazing systems, the intake of ruminants in rain-fed tropical systems is typically below maintenance requirements for part of the year (dry seasons). The relationship between CH4 production and feed intake in animals fed well below maintenance is unexplored, but changes in key digestive parameters in animals fed at low levels suggest that this relationship may be altered. We conducted a study using Boran yearling steers (n 12; live weight: 162·3 kg) in a 4 × 4 Latin square design to assess the effect of moderate to severe undernutrition on apparent digestibility, rumen turnover and enteric CH4 production of cattle consuming a tropical forage diet. We concluded that while production of CH4 decreased (1133·3–65·0 g CH4/d; P < 0·0001), over the range of feeding from about 1·0 to 0·4 maintenance energy requirement, both CH4 yield (29·0−31·2 g CH4/kg DM intake; P < 0·001) and CH4 conversion factor (Ym 9·1–10·1 MJ CH4/MJ gross energy intake; P < 0·01) increased as intake fell and postulate that this may be attributable to changes in nutrient partitioning. We suggest there is a case for revising emission factors of ruminants where there are seasonal nutritional deficits and both environmental and financial benefits for improved feeding of animals under nutritional stress.

Maintenance energy requirements and forage intake of purebred vs. crossbred beef cows1

The objective of this study was to investigate the impacts of cow breed type and age on maintenance requirements, feed energy utilization, and voluntary forage intake. The main effect of breed type included Angus (ANG; n = 32) and Hereford × Angus (HA; n = 27) lactating cows. The main effect of age included 2- and 3-yr-old (YOUNG; n = 29) and 4- to 8-yr-old (MATURE; n = 30) cows. Within breed type and age class, cows were randomly assigned to 1 of 2 pens for a total of 8 pens, each housing 7 to 9 cow/calf pairs. To determine maintenance energy requirements, cows and calves were limit-fed for 105 d to body weight (BW) and body condition score (BCS) stasis. There were no differences between breeds in cow hip height, BW, average milk yield (P &gt; 0.31), diet digestibility, or cow maintenance energy requirement (P = 0.54). Crossbred cows had greater BCS (P &lt; 0.05) throughout the experiment. Efficiency of calf growth was not different between breeds when expressed as feed intake of the cow/calf pair nor as energy intake of the pair per unit of calf BW gain (P ≥ 0.31). Young cows produced less milk per day and per unit of BW0.75 (P &lt; 0.01); however, there was no effect of cow age on maintenance energy requirement, diet digestibility, or efficiency of calf growth (P &gt; 0.10). Subsequently, a 45-d experiment was conducted to determine voluntary low-quality forage intake. Cows were housed in dry-lot pens equipped with shade, windbreaks, and feed bunks with free-choice access to clean water and a chopped hay ration was provided ad libitum to determine forage intake. Daily forage intake was lower (P = 0.05) for HA compared with ANG (123 vs. 132 g/kg BW0.75, respectively) although there was no difference in BW. However, HA cows sustained greater BCS (P &lt; 0.01). There was no difference (P = 0.60) in forage intake per unit of BW0.75 due to cow age. Results indicate similar calf growth efficiency among breed types although crossbred cows maintained greater body energy stores and consumed less low-quality forage during the voluntary intake experiment. These differences could not be attributed to lower maintenance energy requirements. Neither maintenance energy requirement nor calf growth efficiency was different between young and mature cows.