Effect of initial body condition of Boer × Spanish yearling goat wethers and level of nutrient intake on body composition

Small Ruminant Research 73 (2007) 13–26

Effect of initial body condition of Boer × Spanish yearling goat wethers and level of nutrient intake on body composition A.T. Ngwa a , L.J. Dawson b , R. Puchala a , G. Detweiler a , R.C. Merkel a , I. Tovar-Luna a,c , T. Sahlu a , C.L. Ferrell d , A.L. Goetsch a,∗ a

E (Kika) de la Garza American Institute for Goat Research, Langston University, P.O. Box 730, Langston, OK 73050, USA b College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078, USA c Universidad Autonoma Chapingo, Unidad Regional Universitaria De Zonas Aridas, Bermejillo, Durango, Mexico d US Meat Animal Research Center, P.O. Box 166, Clay Center, Nebraska 68933, USA Received 6 February 2006; received in revised form 9 October 2006; accepted 11 October 2006 Available online 9 November 2006

Abstract Yearling Boer × Spanish goat wethers were used to assess effects of initial body condition and subsequent level of feed intake on body composition. Before the experiment, 21 wethers were fed to achieve high body condition score (BCS; 1 to 5, with 1 = extremely thin and 5 = extremely fat) and BW (initially fat; I-F) and 21 were fed for low BCS and BW (initially thin; I-T). During the experiment, I-F wethers were fed low amounts of a pelletized diet and I-T wethers received high amounts. Harvest measures were determined before the experiment (week 0) and after 12 and 24 weeks, with seven animals per initial body condition and time. BCS in Experiment 1 was 3.8, 3.2, 2.6, 1.9, 2.8, and 3.5 (S.E. = 0.11) and live BW was 53.3, 46.2, 42.4, 36.6, 40.1, and 48.2 kg (S.E. = 2.03) for I-F:week 0, I-F:week 12, I-F:week 24, I-T:week 0, I-T:week 1, and I-T:week 2, respectively. There were substantial declines in mass of many internal organs with advancing time for I-F compared with relatively small change for I-T. Examples include the reticulo-rumen (1.03, 0.59, 0.52, 0.87, 0.78, and 0.73 kg; S.E. = 0.041), small intestine (0.59, 0.27, 0.23, 0.55, 0.33, and 0.36 kg; S.E. = 0.021), large intestine (0.40, 0.24, 0.24, 0.33, 0.33, and 0.26 kg; S.E. = 0.017), and liver (0.86, 0.45, 0.42, 0.56, 0.60, and 0.67 kg for I-F:week 0, I-F:week 12, I-F:week 24, I-T:week 0, I-T:week 12, and I-T:week 24, respectively; S.E. = 0.031). Conversely, change in internal or non-carcass fat mass was much greater for I-T versus I-F (5.7, 3.9, 2.8, 0.6, 2.5, and 5.1 kg for I-F-week 0, I-F-week 12, I-F-week 24, I-T-week 0, I-T-week 12, and I-T-week 24, respectively; S.E. = 0.33). Changes in carcass mass of protein (−5.9, −5.3, 7.0, and 5.8 g/day; S.E. = 0.89) and fat (−1.9, 0.2, 21.4, and 26.6 g/day; S.E. = 2.35) were greater (P < 0.05) for I-T versus I-F, as was also true for noncarcass protein (6.1, 0.0, 14.5, and 6.3 g/day; S.E. = 0.91) and fat (−16.3, −10.4, 13.6, and 26.3 g/day for I-F:weeks 1–12, I-F:weeks 1–24, I-T:weeks 1–12, and I-T:weeks 1–24, respectively; S.E. = 2.49). Based on energy concentrations in empty body tissue lost or gained in weeks 1–12 and 1–24 (14.8, 12.1, 19.9, and 26.4 MJ/kg for I-F:weeks 1–12, I-F:weeks 1–24, I-T:weeks 1–12, and I-T:weeks 1–24, respectively; S.E. = 2.13), the energy concentration in weeks 13–24 was 9.4 and 32.9 MJ/kg for I-F and I-T, respectively. In conclusion, the energy concentration in tissue mobilized or accreted by yearling meat goats within certain body condition ranges may not necessarily be the same and appears influenced by initial animal characteristics and subsequent feeding conditions. © 2006 Elsevier B.V. All rights reserved. Keywords: Goats; Body composition; Energy

∗

Corresponding author. Tel.: +1 405 466 6164; fax: +1 405 466 6180. E-mail address: [email protected] (A.L. Goetsch).

0921-4488/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2006.10.013

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A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

1. Introduction

Table 1 Ingredient and chemical composition of the diet

Factors affecting the quantity of energy used for maintenance (MEm ) have marked effect on efficiency of ruminant production. Plane of nutrition influences MEm , but how this effect is addressed by nutrient requirement systems varies. For example, NRC (2000) decreases MEm of beef cattle when body condition score (BCS) is below 3 (5-point scale) and projects increases for BCS above. However, it has been suggested that increases in MEm with high planes of nutrition may not be appropriate unless MEm has been determined by methods such as respiration calorimetry with fasting and a maintenance level of feed intake (Dawson and Steen, 1998). Furthermore, adjusting MEm based on BCS at any one point in time ignores level of feed intake at the present and in the immediate past as well as specific tissues being mobilized or accreted. In this regard, one of the major conditions varying with plane of nutrition that impacts MEm is mass of metabolically active internal organs and tissues. Typically, studies investigating the effects of level of nutrient intake on internal organ mass have been with animals in moderate condition fed to gain or lose BW and have not considered ones initially high or low in BCS. As alluded to above, ruminants are often subjected to periods of restricted nutrient intake, during which time body tissues are mobilized to maintain vital life functions. Subsequently, nutrient intake is elevated to replenish body energy and perhaps protein stores necessary for production. To accurately assess nutrient needs during such times, knowledge of the composition of tissues being lost or gained is necessary. However, for goats there is not a wealth of such information available, as described by AFRC (1998). Therefore, objectives of this experiment were to assess effects of initial body condition and level of subsequent feed intake on body composition of meat goat wethers.

Item

Concentration

Ingredient (%, as fed basis) Dehydrated alfalfa Cottonseed hulls Cottonseed meal Ground corn Wheat middlings Pelletizing agent Trace mineralized salta Salt Yeast Calcium carbonate Ammonium chloride Vitamin A premixb Rumensin 80 premixc

19.98 29.07 15.99 15.99 9.99 5.00 0.50 0.50 1.00 0.95 1.00 0.02 0.01

Chemical constituent Ash (% DM) CP (% DM) NDF (% DM)

9.8 18.6 33.8

2. Materials and methods 2.1. Experiment 1 The experiments were approved by the Langston University Animal Care Committee. In the 5 months preceding Experiment 1, 21 yearling Boer × Spanish yearling (initially approximately 20 months of age) goat wethers were managed to achieve high BW and body condition score (BCS; 1–5, with 1 and 5 extremely thin and fat, respectively), and 21 were managed to have low BW and BCS. These different nutritional planes were achieved with the animals in two pastures, with moderate- to low-quality grass hay available free-choice in each. A pelletized supplement was provided in different

a Contained 95–98.5% NaCl and at least 0.24% Mn, 0.24% Fe, 0.05% Mg, 0.032% Cu, 0.011% Co, 0.007% I, and 0.005% Zn. b Contained 66,200 IU/kg. c 17.6% monensin.

amounts based on change in BW, with the amounts periodically altered. During the 24-week experiment, initially fat (I-F) wethers (ones not harvested at the beginning of the experiment) had restricted access to a pelletized diet (Table 1) to reduce BW and BCS, and initially thin (I-T) wethers had relatively high amounts of feed offered to increase BW and BCS. As animals were weighed every 2 weeks, changes in DM intake (DMI; Table 2) were made to achieve target ADG, although final ADG realized deviated somewhat from initially projected ones. Wethers were treated for internal parasites (Valbazen, SmithKline Beecham Animal Health, West Chester, PA) at the start of the experiment. Wethers resided in 1.05 m × 0.55 m elevated pens with plastic-coated expanded metal floors. Harvest measures were determined immediately before the experiment began (week 0) and after 12 and 24 weeks. Seven IF and seven I-T wethers were harvested at each time over 2-day periods. Wethers harvested at the different times were chosen randomly. Nonetheless, initial BW was slightly greater for animals of week 0 compared with later times; initial empty BW (with values for weeks 12 and 24 based on full BW and the ratio of empty to full or unshrunk BW of animals harvested at week 0) was 44.9, 42.3, 41.8, 27.0, 24.6, and 24.2 kg (S.E. = 1.73) for I-F:week 0, I-F:week 12, I-F:week 24, I-T:week 0, I-T:week 12, and I-T:week 24, respectively. On the morning prior to harvest, wethers were weighed full and BCS was determined by a panel of four individuals, with 0.25-increments. Procedures for determining BCS of Villaquiran et al. (2005a,b) are given in a companion paper (Ngwa et al., 2007). After a 24 h period without feed or water, wethers were harvested via stunning with a captive bolt

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

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Table 2 BW and DMI for yearling Boer × Spanish goat wethers (Experiments 1 and 2) Week

1–2 3–4 5–6 7–8 9–10 11–12 13–14 15–16 17–18 19–20 21–22 23–24b

Initially fata

Initially thina

Initial BW (kg)

DMI (% initial BW)

DMI (kg/day)

Initial BW (kg)

DMI (% initial BW)

DMI (kg/day)

50.8 46.0 45.5 45.1 45.5 45.2 43.1 44.0 43.6 43.6 42.6 42.3

1.07 1.07 1.06 1.05 1.05 1.04 1.03 0.93 0.81 0.70 0.59 0.58

0.54 0.49 0.48 0.47 0.48 0.47 0.44 0.41 0.35 0.31 0.25 0.25

35.8 34.6 35.7 37.0 37.8 40.1 41.3 41.9 44.2 46.3 47.1 47.6

2.63 2.59 2.55 2.52 3.35 3.35 3.35 3.35 3.35 3.35 3.35 3.69

0.94 0.90 0.91 0.93 1.27 1.34 1.38 1.40 1.48 1.55 1.58 1.76

a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, initially fat animals were fed to decrease in BW and condition and initially thin animals were fed to increase. b BW at the end of the experiment was 42.3 and 49.2 kg for initially fat and thin conditions, respectively.

pistol and exsanguination. Blood was collected and weighed. The esophagus was ligated and the head, hooves, and skin were removed and weighed. The rectum was ligated and the entire alimentary tract was removed and weighed before separation into components (esophagus, reticulo-rumen, omasum, abomasum, small intestine, large intestine, and cecum) by ligation and cutting. Components were weighed with digesta then without after washing and blotting some with paper towels. Non-carcass or internal fat was the sum of visceral and perirenal depots. Pools of weighed non-carcass components (blood, head, hide, organs, and fat) and the carcass were ground (Model 801 Autogrinder; Austio Company, Astoria, OR) separately three times sequentially through each of three plates with different apertures (i.e., 10, 5, and 2 mm). After the final grind, the sample was hand-mixed and duplicate 250 g aliquots were collected and stored at −20 ◦ C. Carcass and non-carcass pool samples were analyzed for DM by lyophilization (Model CRVP-195P Dura Stop; FTS Systems, Stone Ridge, NY). After drying, samples were reground in a blender (Model 36BL23 HGBSS; Waring, New Hartford, CT) and analyzed for CP, ash (AOAC, 1990), and fat. Fat was determined by supercritical fluid extraction (Model SFX 220; ISCO, Lincoln, NE). However, there was an equipment problem in fat analysis detected after all samples had been analyzed. After correcting the problem, the 24-week samples were re-analyzed. Samples from 0 and 12 weeks could not also be re-analyzed because they had been inadvertently discarded. The average fat concentration (empty BW basis) in 24-week samples re-analyzed were 23.0 (S.E. = 0.60) and 29.3% (S.E. = 1.37) in carcass and noncarcass pools, respectively, which were quite similar to the difference between 100 and the sum of water, protein, and ash levels (carcass: 24.7% 0.64; noncarcass: 31.1% 1.34). In addition, fat concentrations at 24 week determined by the two methods were closely related (r = 0.97; P < 0.0001). Hence, the latter values

were employed for all samples. Energy concentrations of 39.3 and 23.1 MJ/kg were assumed for fat and protein, respectively (ARC, 1980). Concentrations of chemical constituents in tissue being mobilized or accreted are presented for weeks 1–12 and 1–24 based on average week 0 values for I-F and I-T expressed on a full BW basis and full BW of animals harvested at weeks 12 or 24. Values for weeks 13–24 are not presented in tables because for a small number of animals in that period changes in empty BW and mass of the constituents were small, resulting in high variability. Values for weeks 13–24 based on differences between means for weeks 1–12 and 1–24 are given in the text. ME intake (MEI) was derived from average DMI within each 12-week period applied to ME concentrations determined in Experiment 2 for the same treatments, with values used in weeks 1–12 averages of measures in the early and middle portions of Experiment 2 and those in weeks 13–24 averages of middle and late segments. An efficiency of energy utilization (k) was estimated. For I-T, k is an efficiency of use of dietary energy for maintenance and gain, determined by dividing net energy (NE) by MEI. NE was the sum of energy gain or recovered energy (RE) and NE for maintenance (NEm ). NEm was based on average fasting EE expressed relative to full BW in Experiment 2 applied to full BW in Experiment 1. Values from Experiment 2 were averages of means in early, middle, and late segments of the experiment for each initial body condition treatment. Average unshrunk BW during weeks 1–12 and 13–24 of Experiment 1 were used. For I-F, 11 of the 14 observations entailed negative RE as expected. However, for three animals in weeks 13–24, RE was slightly greater than 0. For the 11 animals with negative RE, k is an efficiency of use of dietary ME for maintenance. NEm was calculated as for I-T animals. NEm arising from mobilized tissue was estimated assuming an efficiency of use of mobilized tissue energy for maintenance of 84% (AFRC, 1993). NEm for the three animals with posi-

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A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

tive RE and NEm from the diet for the other 11 animals were divided by MEI to estimate k. Data were analyzed as a 2 × 3 or 2 × 2 factorial arrangement of treatments by GLM procedures of SAS (1990). When the interaction between initial body condition and time was nonsignificant and a main effect was significant, main effect means are presented in tables. Means were separated by least significant difference. 2.2. Experiment 2 An additional 12 wethers, six I-F and six I-T, were managed before the experiment in the same manner as those of Experiment 1. However, they began Experiment 2 1 week before animals of Experiment 1, at which time they were placed on the different planes of nutrition (i.e., low DMI for I-F and high DMI for I-T). The wethers were in three sets, with two I-F and two I-T per set. During 10-day measurement periods for each set, wethers resided in metabolism crates. Total feces and urine collections were on days 1–6. A 10% aliquot of fecal output was used to form a composite sample. Urine was collected in plastic bottles containing 10 ml of a 10% (v/v) sulfuric acid solution, with a composite also formed from 10% subsamples. Feed was sampled daily. Feed and fecal samples were dried in a forced-air oven at 55 ◦ C for 48 h then ground in a Willey mill to pass a 1 mm screen. Feed and fecal samples were analyzed for DM, ash, gross energy by bomb calorimetry, N (AOAC, 1990), and ADF ash (filter bag technique; ANKOM Technology Corp., Fairport, NY), and feed was analyzed for NDF (ANKOM Technology Corp.) Urine samples were assayed for DM (lyophilization), and nitrogen and energy concentrations were determined with lyophilized samples. On days 5–6, gas exchange measures were performed, with procedures described by Tovar-Luna et al. (2007). Briefly, prior to measures wethers were placed in metabolism crates fitted with training head-boxes for adaptation. Oxygen consumption and production of carbon dioxide and methane were determined with an open-circuit respiration calorimetry system (Sable Systems, Las Vegas, NV) with four head-boxes placed in a calorimetry room. Oxygen concentration was analyzed using a fuel cell FC-1B oxygen analyzer (Sable Systems). Carbon dioxide and methane concentrations were measured using infrared analyzers (FC-1B for CO2 and MA-1 for CH4 ; Sable Systems). Air was first analyzed for CH4 then for CO2 and O2 . Prior to the gas exchange measurement periods, validity and accuracy of expired CO2 and inspired O2 flows were checked with alcohol combustion (average 101.3 1.1 and 100.3 1.6% of expected CO2 production and O2 consumption, respectively). Before each test analyzers were calibrated with reference gas mixtures (19.5 and 20.5% O2 , 0.0 and 1.5% CO2 and 0.0 and 0.3% CH4 ). On days 7–10, wethers were fasted, with gas exchange measures and urine collection on days 9–10. Set 2 animals began the collection period 2 days after set 1, thus ending on day 12. Set 3 began fecal and urine collections on day 9, so that gas exchange measures during fasting were on days 17–18. In addition to measures at this “Early” time, they were repeated in weeks 11–13 (Middle), and 22–24 (Late).

MEI was calculated from gross energy intake and feces, urine, and methane energy losses. For the fecal energy loss, fecal samples were inadvertently dried without determining DM concentration. Hence, ADF ash was used as an internal marker to estimate fecal output. EE was estimated based on the Brouwer (1965) equation with oxygen consumption and carbon dioxide and methane production obtained on days of gas exchange measurement and urinary N excretion determined during both the fed and fasting segments. EE and MEI were expressed relative to BW at the beginning of the determination of fasting EE. k was estimated by regressing the difference between MEI and EE (i.e., RE) against MEI when fed and fasting. In this experiment, for I-T k is an efficiency of use of dietary energy for maintenance and gain, and for I-F k is an efficiency of use of dietary ME and mobilized tissue energy for maintenance. Data were analyzed by a mixed model (Littell et al., 1996), with fixed effects of initial body condition and time (repeated measure) and the random effect of animal. Presentation of main effect means and means separation were as described for Experiment 1.

3. Results 3.1. Experiment 1 3.1.1. BCS, BW, carcass, and non-carcass components Changes in BW and BCS were large; however, values for I-F at 24 week did not reach those of I-T at 0 week, as was also true for I-T at 24 week compared with I-F at 0 week (Table 3). Digesta fill was similar among body condition treatments and times. Expressed relative to empty BW fill was greatest among times for I-T in week 0 (P < 0.05) and was greater (P < 0.05) for I-F animals at week 24 than 0. Carcass weight as a % of empty BW increased as the experiment advanced (Table 3). Hence, for I-F with limited DMI the decrease in non-carcass mass was greater than the decline in mass of the carcass. For I-T, as time progressed with high DMI the increase in carcass mass was greater than in non-carcass tissues. Thus, mass of non-carcass organs/tissues was relatively more responsive than carcass mass to the limited nutritional plane and carcass mass was more responsive to the high nutritional plane. Most change in mass in grams of the reticulo-rumen occurred by 12 week for both I-F and I-T, with mass at 12 and 24 week being similar (Table 3). The magnitude of change was considerably greater for I-F than for IT, with mass in grams of the reticulorumen for I-F at 24 week 50% of that at week 0. Differences in mass in grams of the abomasum were relatively similar to those in the reticulorumen. Conversely, though effects

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

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Table 3 Effects of initial body condition and level of feed intake on harvest measures of yearling Boer × Spanish goat wethers (Experiment 1) Itemc

Initially fat (I-F)a Week 0

Week 12

Week 24

Week 0

Week 12

Week 24

BCS BW Full (kg) Shrunk (kg) Empty (kg) Empty (% full)

3.8d

3.2c

2.6b

1.9a

2.8b

3.5cd

0.11

53.3d 50.6d 44.9d 84.3c

46.2c 43.7c 38.2c 82.5bc

42.4bc 40.2bc 34.6bc 81.5b

36.6a 34.3a 27.0a 73.7a

40.1ab 37.8ab 32.2b 80.4b

48.2cd 45.1cd 39.7c 82.4bc

2.03 1.99 1.70 0.97

Digesta (fill) kg % Empty BW

8.4 18.7a

8.1 21.4ab

8.0 23.3b

9.6 35.8c

7.9 24.5b

8.5 21.4ab

0.61 1.55

Carcass kg % Empty BW % Full BW

24.7d 55.0 47.3c

21.6c 56.8 45.8bc

20.3bc 58.4 46.6bc

14.7a 54.1 40.8a

17.7b 55.1 44.2b

22.3cd 56.2 46.4bc

1.02 0.61 0.84

Noncarcass kg % Empty BW

20.2c 45.0

16.5cd 43.2

14.3ab 41.6

12.3a 45.9

14.5bc 44.9

17.4d 43.8

0.73 0.61

84 516a 322 128a 227a 240a 38 2.8b 419a 165a 68 287 89a 69 1.5 2.9 3.3ab 1.2

46 865c 111 196c 546c 325b 42 0.6a 556b 185b 35 347 101ab 61 1.3 3.0 2.8a 1.2

68 778bc 93 187bc 325b 325b 34 2.5b 604bc 156a 55 272 105b 64 1.6 2.9 3.4ab 1.1

163 729b 113 191c 364b 264a 33 5.1d 669c 169ab 68 276 103ab 66 1.3 3.0 3.5c 1.3

37.3 41.2 66.3 10.0 20.5 17.2 3.0 0.33 30.7 8.9 6.8 27.1 5.1 7.1 0.10 0.10 0.21 0.61

1.7 32.4d 4.2 7.4 20.5d 12.3d 1.6d 22.9a 20.8d 7.0c 1.3 12.6b 3.8c 2.3 49.1e 111.9c 105.0c 42.6c

2.1 24.1c 2.9 5.8 10.2b 10.2c 1.1bc 74.7b 18.8c 4.9ab 1.7 8.5a 3.3b 2.0 48.8de 91.4b 103.8c 33.9b

4.2 18.3b 2.8 4.8 9.2b 6.6a 0.8a 127.9a 16.8b 4.3a 1.7 7.0a 2.6a 1.6 33.7a 74.7a 88.9ab 32.0ab

1.02 0.87 1.88 0.32 0.53 0.50 0.09 6.70 0.55 0.29 0.21 0.62 0.13 0.16 2.02 2.84 2.96 1.39

Non-carcass component mass in g or kg Esophagus (g) 57 55 RR (g) 1030d 589a Omasum (g) 115 187 Abomasum (g) 229d 161b SI (g) 594c 269ab LI (g) 379c 240a Cecum (g) 46 32 Fat (kg) 5.7d 3.9c Liver (g) 864d 454a Heart (g) 252c 162a Trachea (g) 51 53 Lungs (g) 328 268 Kidneys (g) 138c 90a Spleen (g) 97 78 Blood (kg) 1.6 1.6 Head (kg) 3.4 3.2 Skin (kg) 3.9c 4.0c Hooves (kg) 1.3 1.2

Initially thin (I-T)a

Non-carcass component mass in g/kg empty BW Esophagus 1.3 1.5 2.5 RR 23.0c 15.5a 15.1a Omasum 2.6 4.6 9.8 Abomasum 5.1 4.3 3.8 SI 13.3c 7.2a 6.6a LI 8.4b 6.4a 6.9a Cecum 1.0abc 0.9ab 1.1c Fat 128.0d 100.8c 79.6b Liver 19.3c 12.0a 12.1a Heart 5.7b 4.3a 4.8a Trachea 1.1 1.4 2.0 Lungs 7.4a 7.1a 8.3a Kidneys 3.1b 2.4a 2.6a Spleen 2.1 2.0 2.0 Blood 36.4ab 41.5bc 43.1cd Head 76.2a 84.5b 84.2b Skin 86.1a 104.6c 95.9b Hooves 29.7a 31.2ab 35.1b

S.E.

Weekb

S.E.

0

12

24

54.6a

56.0b

57.3c

45.4c

44.0b

44b

43a 338b

Body conditionb I-F

I-T

S.E.

0.43

58.8b

55.1a

0.35

42.7a

0.43

43.2a

44.9b

0.35

33a

36a

2.1

54a 270a

68b 281a

4.8 19.2 81b

64a

4.1

3.2b

3.1ab

2.9a

0.07

3.2b

3.0a

0.06

6.3c

5.0b

4.3a

0.22

4.39a

6.0b

0.18

1.2a

1.6ab

1.9b

0.15

a,b,c,d: Means in a row within body condition × week, week, and initial body condition groupings without a common letter differ (P < 0.05). a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, I-F were fed to decrease in BW and condition and I-T were fed to increase. b Main effect means for week and body condition appear when the week × body condition interaction was nonsignificant (P > 0.05) and a main effect was significant (P < 0.05). c BCS = body condition score (1–5; 1 and 5 = extremely thin and fat, respectively); RR = reticulo-rumen, SI = small intestine; LI = large intestine.

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A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

were not significant, numerically mass in grams of the omasum for I-F increased as the experimental period advanced. As occurred for the reticulorumen, small intestinal mass in grams for I-F decreased greatly from weeks 0 to 12, without further change from weeks 12 to 24 (Table 3). But, somewhat different from reticuloruminal mass, mass in grams of the small intestine for I-T also decreased considerably from weeks 0 to 12 despite high feed intake compared with that before the experiment. Mass in grams of the large intestine decreased from 0 to 12 weeks, but the magnitude of change for I-F was smaller than in mass of the small intestine. For I-T, there was a slight decrease in large intestinal mass in grams from 12 to 24 weeks. Cecal mass in grams was greater (P < 0.05) at weeks 0 versus 12 and 14. Non-carcass fat mass in kilograms declined (P < 0.05) for I-F as the experiment advanced, with a difference of 2.9 kg between 0 and 24 weeks (Table 3). The magnitude of change for I-T was much greater, with mass at 24 week 4.5 kg greater than at week 0. As opposed to some other internal organs/tissues, internal fat mass differed (P < 0.05) among each measurement time. Liver mass in grams largely corresponded to that of the reticulorumen. There was a marked decrease for I-F from weeks 0 to 12, without significant change to week 24. Liver mass in grams for I-T was not appreciably different among times, but was greater (P < 0.05) at week 24 versus 0. Most likely due to associated fat, heart mass in grams for I-F was greater (P < 0.05) at week 0 versus 12. Lung mass in grams was greater (P < 0.05) at week 0 than 12 and 24. Kidney mass in grams was similar among times for I-T, but for I-F was greater (P < 0.05) at week 0 versus 12 and 24. Mass in grams of the spleen was greater (P < 0.05) for I-F than for I-T. Blood and hoof mass in kilograms were similar among treatments. Mass in kilograms of the head was greater (P < 0.05) for week 0 versus 24 and for I-F versus I-T. Skin mass in kilograms was affected by nutrient restriction more slowly than by high nutrient intake, being greater for I-F at week 0 and 12 versus 24 and for I-T at week 24 but not for week 12 compared with week 0. For brevity, mass relative to empty BW (Table 3) for only a few select non-carcass components will be highlighted. Reticulo-ruminal mass was greater (P < 0.05) at 12 and 24 weeks than at 0 week for I-T and for I-F ranked (P < 0.05) week 0 > 12 > 24. Small intestinal mass for both I-F and I-T animals was greater (P < 0.05) at week 0 versus 12 and 24 and was less for I-F versus I-T at each time. Internal fat mass ranked (P < 0.05) I-T:week 0 < IF:week 24 and I-T:week 12 < I-F:week 12 < I-F:week 0. Liver mass for I-F was greater (P < 0.05) at week 0 than

at weeks 12 and 24 and for I-T ranked (P < 0.05) weeks 0 > 12 > 24. 3.1.2. Mass and concentrations of chemical constituents Carcass ash concentration was similar among times for I-F but declined (P < 0.05) with advancing time for I-T (Table 4). Non-carcass ash concentration ranked (P < 0.05) weeks 12 > 24 > 0 and was greater (P < 0.05) for I-F than for I-T. Ash concentration in the empty body was lower (P < 0.05) for I-F:weeks 0 versus I-F:week 12 and was lowest among times (P < 0.05) for I-T at week 24. Protein concentrations in the carcass, noncarcass pool, and empty body were not influenced by initial body condition × time interactions; however, effects of time were significant. Carcass protein concentration decreased (P < 0.05) as the experiment progressed, whereas protein concentration in the non-carcass pool ranked (P < 0.05) week 12 > 24 > 0. These differences resulted in an empty body protein concentration greatest among times (P < 0.05) for week 12. For I-F, differences in water concentration among times were nonsignificant or of relatively small magnitude. Conversely, for I-T water concentration in the carcass, non-carcass pool, and empty body decreased (P < 0.05) as time advanced. Changes as time progressed in fat concentration in the two pools for I-F wethers were in opposite directions (increasing for carcass and decreasing for non-carcass), resulting in no differences among times in empty body values (Table 4). For I-T, in both carcass and non-carcass pools fat concentration markedly increased (P < 0.05) as the experiment advanced. Energy concentration in the carcass, non-carcass pool, and empty body were either similar or magnitudes of difference were relatively small. Conversely, energy concentration in both pools and the empty body for I-T increased (P < 0.05) as the experimental period progressed. The ratio of water to protein in the carcass was not significantly influenced by body condition treatment or harvest time (Table 4). Conversely, the ratio for the noncarcass pool ranked (P < 0.05) I-T:week 0 > I-F:week 0 > I-F and I-T in weeks 12 and 24. There were also differences in the ratio for the empty body, being greatest (P < 0.05) for I-T:week 0 and with a greater (P < 0.05) value for I-F:week 0 than for I-F:week 12 and I-T:week 12. 3.1.3. Tissue loss or gain Table 5 lists daily change in mass of chemical constituents of carcass and non-carcass pools and the whole body. These provide a more accurate description of change in mass than mass at weeks 0, 12, and 24 given in

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

19

Table 4 Effects of initial body condition and level of feed intake on tissue mass and composition in yearling Boer × Spanish goat wethers (Experiment 1) Item

Initially fat (I-F)a

Initially thin (I-T)a

S.E.

Week 0 Week 12 Week 24 Week 0 Week 12 Week 24

Weekb 0

S.E. 12

24

Body conditionb I-F

I-T

S.E.

Carcass mass Ash (kg) Protein (kg) Water (kg) Fat (kg) Energy (MJ)

0.80 3.88d 15.25c 5.25c 296c

0.69 3.16bc 12.59bc 4.76c 260c

0.58 2.72ab 11.62abc 4.90c 255c

0.64 2.52a 10.49a 1.18a 105a

0.65 2.90abc 11.29ab 2.91b 181b

0.61 3.24c 12.93c 5.55c 293c

0.040 0.72b 0.67ab 0.60a 0.161 0.500 0.331 15.2

Non-carcass mass Ash (kg) Protein (kg) Water (kg) Fat (kg) Energy (MJ)

0.37 2.54bc 10.62b 6.17d 301d

0.48 2.90c 9.14a 4.45c 242c

0.37 2.35b 8.02a 4.01c 212bc

0.23 1.54a 8.49a 1.88a 110a

0.34 2.61bc 8.69a 2.86b 173b

0.34 2.42bc 8.50a 6.15d 298d

0.034 0.30a 0.41b 0.170 0.476 0.330 15.2

0.36ab 0.024 0.41b 0.31a 0.020

Empty body mass Ash (kg) 1.16 Protein (kg) 6.42d Water (kg) 25.87c Fat (kg) 11.42d Energy (MJ) 597d

1.68 6.06cd 21.73b 9.20c 502c

0.95 5.07b 19.64ab 8.91c 467c

0.87 4.07a 18.98a 3.06a 214a

0.99 5.50bc 19.98ab 5.76b 354b

0.95 5.66bcd 21.44ab 11.70d 591d

0.060 1.02b 1.08b 0.301 0.905 0.616 28.9

0.95a

0.042

Carcass composition Ash (%) 3.2b Protein (%) 15.4 Water (%) 60.7b Fat (%) 20.7c Energy (MJ/kg) 11.7c

3.3b 14.9 59.6ab 22.2cd 12.2cd

3.0ab 13.8 58.7a 24.5d 12.8d

4.3c 16.9 70.7d 8.1a 7.1a

3.7b 16.3 63.9c 16.2b 10.1b

2.7a 14.5 57.9a 24.8d 13.1d

0.16 0.40 0.76 0.98 0.34

16.2c 15.6b

14.2a

0.28

14.7a 15.9b 0.23

Non-carcass composition Ash (%) 1.9 Protein (%) 12.8 Water (%) 54.0b Fat (%) 31.4d Energy (MJ/kg) 15.3c

2.8 17.0 54.2b 26.0c 14.2c

2.5 15.9 54.5b 27.0c 14.3c

1.9 12.6 69.9d 15.6a 9.0a

2.4 18.0 60.2c 19.4b 11.8b

2.0 13.9 48.9a 35.2c 17.1d

0.15 0.63 0.99 1.28 0.43

1.9a 2.6c 12.7a 17.5c

2.3b 14.9b

0.11 0.44

2.4b

Empty body composition Ash (%) 2.6a Protein (%) 14.3 Water (%) 57.7b Fat (%) 25.4c Energy (MJ/kg) 13.3c

3.1bc 15.9 57.2b 23.9c 13.1c

2.8ab 14.7 56.9b 25.6c 13.5c

3.2c 15.0 70.3d 11.4a 8.0a

3.1c 17.1 62.2c 17.6b 10.9b

2.4a 14.3 54.0a 29.3d 14.8d

0.10 0.38 0.76 0.96 0.34

14.6a 16.5b

14.8a

0.27

Water:protein ratio Carcass 3.95 Non-carcass 4.27b Empty body 4.06b

4.00 3.19a 3.61a

4.28 3.43a 3.88ab

4.20 5.73c 4.72c

3.93 3.36a 3.65a

4.03 3.53a 3.81ab

0.114 0.197 0.106

0.029

2.1a

0.09

a,b,c,d: Means in a row within body condition × week, week, and initial body condition groupings without a common letter differ (P < 0.05). a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, I-F were fed to decrease in BW and condition and I-T were fed to increase. b Main effect means for week and body condition appear when the week × body condition interaction was nonsignificant (P > 0.05) and a main effect was significant (P < 0.05).

Table 4 because those values are for the different animals harvested at the three times. The carcass of I-F animals lost a small amount of ash each day and there was slight gain for I-T (Table 5). Gain of ash by non-carcass tissues of I-T was similar

to that by the carcass, although more ash was accreted in non-carcass tissues of I-F than I-T animals. About the same quantity of carcass protein was mobilized by I-F as was accreted by I-T. Conversely, daily change in non-carcass tissue protein mass was greater for I-T

20

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

Table 5 Effects of initial body condition and level of feed intake on daily tissue loss or gain by yearling Boer × Spanish goat wethers (Experiment 1) I-Fa

Item

Week 1–12 Empty body Change Wet tissue (g) −49.0 Ash (g) 0.8 Protein (g) 0.3 Fat (g) −18.2 Water (g) −31.9 Energy (MJ) −0.71 Tissue concentration Ash (%) −1.8a Protein (%) −1.0a Fat (%) 38.3a Water (%) 64.5 Energy (MJ/kg) 14.8ab Carcass Wet tissue (g) Ash (g) Protein (g) Fat (g) Water (g) Energy MJ MJ/kg

−30.2 −0.8 −5.9 −1.9 −21.6 −0.21 7.3

Noncarcass tissues Wet tissue (g) −18.8 Ash (g) 1.6 Protein (g) 6.1 Fat (g) −16.3 Water (g) −10.3 Energy MJ MJ/kg

−0.50 27.9bc

I-Ta

S.E.

Week 1–24

Week 1–12

Week 1–24

−42.9 −0.8 −5.3 −10.1 −26.7 −0.52

90.3 2.4 21.5 35.0 31.4 1.87

92.4 1.0 12.0 53.1 26.2 2.37

6.57 0.36 1.25 4.47 3.92 0.185

1.7b 12.8b 23.2a 62.3 12.1a

2.6b 24.8c 35.9a 36.6 19.9b

1.2b 13.1b 59.3b 26.4 26.4c

0.72 2.19 5.95 4.89 2.13

48.8 0.8 7.0 21.4 19.6

53.1 0.2 5.8 26.6 20.5

4.33 0.31 0.89 2.35 2.76

1.01 21.0

1.18 23.1

0.094 2.07

41.5 1.6 14.5 13.6 11.9

39.3 0.8 6.3 26.6 5.6

3.29 0.21 0.91 2.49 2.13

0.87 20.3ab

1.19 31.0c

0.102 3.03

−21.6 −1.0 −5.3 0.2 −15.6 −0.11 4.5 −21.3 0.2 0.0 −10.4 −11.1 −0.41 19.1a

Weekb

S.E.

1–12

1–24

1.6b 10.9b 8.4a

0.1a 3.4a 21.5b

0.25 0.89 3.16

Body conditionb I-F

I-T

−45.9a 0.0a −2.5a −14.1a −29.3a −0.61a

91.3b 1.7b 16.8b 44.1b 28.8b 2.12b

4.65 0.25 0.89 3.16 2.77 0.131

63.4b

31.5a

3.46

−25.9a −0.9a −5.6a −0.8a −18.6a

50.9b 0.5b 6.4b 24.0b 20.0b

3.06 0.22 0.63 1.66 1.95

1.09b 22.0b

0.066 1.46

−20.1a

40.4b

2.33

3.1a −13.3a −10.7a

10.4b 20.1b 8.7b

0.64 1.76 1.50

−0.16a 5.9a

1.6b 10.3b

0.5a 3.1a

0.15 0.64

S.E.

−0.45a

1.03b

0.072

a,b,c,d: Means in a row within body condition × week, week, and initial body condition groupings without a common letter differ (P < 0.05). a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, I-F were fed to decrease in BW and condition and I-T were fed to increase. b Main effect means for week and body condition appear when the week × body condition interaction was nonsignificant (P > 0.05) and a main effect was significant (P < 0.05).

versus I-F, with positive means for both initial body condition treatments. Also, non-carcass protein accretion was much greater in weeks 1–12 versus 1–24. Based on differences in values for weeks 1–12 and 1–24, noncarcass tissues of I-F animals lost 6.1 g/day of protein in weeks 13–24, and non-carcass tissues for I-T in weeks 13–24 did not accrete protein. The carcass of I-F animals did not incur fat mobilization throughout the experiment, compared with appreciable accretion for I-T. Daily change in non-carcass tissue fat mass was, as expected, greater (P < 0.05) for I-T versus I-F. Non-carcass tissue fat mobilization was 4.5 g/day for I-F in weeks 13–24

and accretion by I-T was 39.6 g/day. Daily change in water mass made up a very large portion of the carcass being mobilized by I-F (i.e., 72% in weeks 1–12 and 1–24) and less of carcass accreted by I-T (i.e., 40 and 39% in weeks 1–12 and 1–24, respectively). Change in water mass by non-carcass tissues constituted less of change in empty body mass, being 55 and 52% of tissue mobilization in weeks 1–12 and 1–24 by I-F and 29 and 14% of tissue accretion in weeks 1–12 and 1–24 by I-T, respectively. The energy concentration in carcass tissue mobilized or accreted was considerably greater for I-T versus I-F, with no differences between weeks

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

21

Table 6 Effects of initial body condition and level of feed intake on digestibilities, urinary energy, methane emission, and dietary ME concentration for yearling Boer × Spanish goat wethers (Experiment 2) Item

Initially fat (I-F)a

Initially thin (I-T)a

S.E.

Early

Middle

Late

Early

Middle

Late

Intake DM (g/day) OM (g/day) N (g/day) Energy (MJ/day)

547b 494b 16.3b 9.8b

430ab 388ab 12.8ab 7.7ab

249a 225a 7.4a 4.4a

1014c 915c 30.1c 18.1c

1445d 1304d 42.9d 25.8d

1206c 1088c 35.8c 21.5c

Digestibility (%) DM OM N Energy

60.2 62.4 75.4 60.2

63.2 65.8 78.8 63.6

59.2 62.7 75.8 60.6

58.5 59.9 75.9 58.2

59.4 61.5 76.7 59.7

51.6 53.9 71.8 51.6

Energy excretion/emission (MJ/day) Urinary energy 0.31 0.21 Methane 0.52 0.40

0.09 0.42

0.46 0.61

0.43 0.43

ME (MJ/kg DM)

8.7a

9.3ab

10.7b

9.2ab

10.0b

Timeb,c

S.E.

Early

Middle

Late

1.41 1.48 1.07 1.54

59.3ab 61.1ab 75.7ab 59.2ab

61.3b 63.7b 77.8b 61.7b

55.4a 58.3a 73.8a 56.1a

0.31 0.57

0.046 0.061

0.39a

0.32a

0.20b

8.5a

0.30

Body conditionc I-F

I-T

S.E.

1.00 1.04 0.76 1.12

60.9b 63.3b 76.7b 61.5b

56.5a 58.4a 74.8a 56.5a

0.83 0.87 0.61 0.89

0.032

0.20a

0.40b

0.265

76.8 69.4 2.34 1.39

a,b,c,d: Means in a row within body condition × time, time, and initial body condition groupings without a common letter differ (P < 0.05). a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, I-F were fed to decrease in BW and condition and I-T were fed to increase. b Early = week 1–3; Middle = week 11–13; Late = week 22–24. c Main effect means for time and body condition appear when the time × body condition interaction was nonsignificant (P > 0.05) and a main effect was significant (P < 0.05).

1–12 and 1–24. Conversely, there was an interaction (P < 0.05) between initial body condition and week in the concentration of energy in non-carcass tissues mobilized or accreted. For I-F, the concentration was greater (P < 0.05) in weeks 1–12 versus 1–24, and there was an opposite difference (P < 0.05) for I-T. Considering differences between weeks 1–12 and 1–24, the energy concentration in weeks 13–24 was 10.3 MJ/kg for I-F and 41.7 MJ/kg for I-T. Similar to non-carcass tissues, there was an interaction (P < 0.05) between initial body condition and week in energy concentration in empty body tissue mobilized or accreted (Table 5). Values were similar between weeks for I-F and for I-T were greater for weeks 1–24 versus 1–12; I-T values were greater than for I-F in weeks 1–24. The energy concentration in empty body tissue mobilized in weeks 13–24 was 9.4 MJ/kg and that in tissue accreted by I-T was 32.9 MJ/kg. Ash and protein concentrations in empty body tissues of I-F mobilized in weeks 1–12 were not different from 0. There were interactions between initial body condition and week in concentrations of ash, protein, and fat in empty body tissue mobilized or accreted (P < 0.05). Protein concentration in empty body tissue mobilized by I-F changed from essentially 0 in weeks 1–12 to 26.6% in weeks 13–24, and the level of fat decreased from 38.3 to 8.1%.

Opposite changes occurred for tissue accreted by I-T; protein concentration decreased from 24.8% in weeks 1–12 to approximately 0 in weeks 13–24, and the level of fat increased from 35.9 to 82.7%. 3.1.4. Efficiency of energy use k was 81, 106, 52, and 48% (S.E. = 2.3) for I-F:weeks 1–12, I-F:weeks 13–24, I-T:weeks 1–12, and I-T:weeks 13–24, respectively, averaging 94% for I-F and 50% for I-T (S.E. = 1.6). If the three I-F observations with positive RE are omitted, k becomes 103% and not different from 100%. 3.2. Experiment 2 Apparent total tract digestibilities of DM, OM, and energy were less (P < 0.05) in the Late versus Middle period of measurement or time (Table 6). Reasons for this difference may in part involve the relatively high contribution of endogenous DM to feces for I-F in the Late period because of limited DMI. However, reasons for the difference between times for I-T may not be related to level of feed intake, since DMI was less at the Late than Middle time. As expected, because of lower DMI and presumably shorter digesta retention time in the digestive tract, digestibilities were greater for I-F

22

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

Table 7 Effects of initial body condition and level of feed intake on body condition score (BCS), BW, ME intake, energy expenditure, recovered energy (RE), and efficiency of ME utilization (k) by yearling Boer × Spanish goat wethers (Experiment 2) Initially fat (I-F)a

Item

BCSd

Initially thin (I-T)a

S.E.

Early

Middle

Late

Early

Middle

Late

3.7c

3.1b

2.4a

2.1a

2.9b

3.3bc

0.16

46.1cd 44.3cd

45.5cd 42.7c

41.1ab 39.1b

33.2a 31.9a

41.6bc 38.2bc

50.7d 46.2d

3.23 2.82

5.04b 294b

4.27ab 256ab

2.18a 152a

9.48c 664c

14.46d 875e

10.35c 548d

0.80 24.9

5.05b 294

4.37b 262

3.16a 204

4.44b 321

4.28b 274

4.54b 257

6.48b 379

5.97ab 355

4.45a 285

7.39bc 538

8.44c 539

8.47c 473

−1.44a

−1.70a

−2.26a

2.09b

6.02c

1.88b

0.493

70.5

60.3

40.4

66.7

64.6

60.0

4.85

Timeb,c

S.E.

Early

Middle

Late

0.34 14.8

307c

268b

231a

0.58 19.9

458b

447b

379a

68.2b

62.4b

50.2a

Body conditionc I-F

I-T

S.E.

10.5

253a

284b

8.5

14.0

340a

517b

11.4

57.0

63.8

BWd Fed Fasting ME intake MJ/day kJ/kg BW0.75,e Energy expenditure Fasting MJ/day kJ/kg BW0.75,f Fed MJ/day kJ/kg BW0.75,f REg

(MJ/day)

kh (%)

3.43

2.79

a,b,c,d: Means in a row within body condition × time, time, and initial body condition groupings without a common letter differ (P < 0.05). a Animals had been managed in the 5 months preceding the experiment to be in different levels of body condition. During the 24-week experiment, I-F were fed to decrease in BW and condition and I-T were fed to increase. b Early = weeks 1–3; Middle = weeks 11–13; Late = weeks 22–24. c Main effect means for time and body condition appear when the time × body condition interaction was nonsignificant (P > 0.05) and a main effect was significant (P < 0.05). d 1–5 (1 and 5 = extremely thin and obese, respectively). e BW determined at the beginning of the 2-day measurement period for energy expenditure when fasting. f Energy expenditure was expressed relative to fasting BW. g RE was estimated as the difference between ME intake and energy expenditure. h For I-T, k is an efficiency of use of dietary energy for maintenance and gain; for I-F, k is an efficiency of use of dietary ME and mobilized tissue energy for maintenance. k was determined by regressing RE against ME intake.

versus I-T. Urinary energy excretion as expected was greater (P < 0.05) for I-T than for I-F. Urinary energy also was less (P < 0.05) in the Late measurement time compared with earlier ones. The low level of DMI for I-F animals at the Late time would have contributed to this difference, although factors responsible for I-T animals are unclear. Methane emission was similar among initial body conditions and measurement times. Fasting and fed EE expressed in MJ/day were influenced by initial body condition × time interactions, although values in kJ/kg BW0.75 were not (Table 7). Fasting EE in MJ/day for I-F was lowest among times for Late (P < 0.05), which probably relates to lowest DMI. Fed EE in MJ/day for I-F was lower (P < 0.05) for the Late than for the Early time, with the Middle mean being intermediate (P > 0.05). Neither fasting nor fed EE in MJ/day for I-T animals differed among times. Fasting EE in MJ/day for I-T animals was similar to Early and Middle values for I-F. But, fed values either tended to be (Early)

or were greater (P < 0.05; Middle and Late) than for I-T. Expressed relative to BW0.75 , EE was greater both during fasting and in the fed state for I-T versus I-F, although the difference was much greater when fed (i.e., 177 versus 31 kJ/kg BW0.75 and 52 versus 12%). Fasting EE relative to BW0.75 ranked (P < 0.05) Early > Middle > Late and fed EE was greater (P < 0.05) for the Early than for Middle and Late times. For I-F animals, declining DMI as the experiment progressed probably contributed to this change. Incomplete consumption of all offered feed by some I-T animals in the Late measurement period may have been partially responsible for these differences as well. RE was similar among times for I-F, and all values were lower (P < 0.05) than for I-T. The interaction between initial body condition and measurement time in k approached significance (P < 0.08), as was also the case for the effect of initial body condition (P < 0.11). k was, however, lower (P < 0.05) in the Late than Early and Middle times, but this difference was the result pri-

A.T. Ngwa et al. / Small Ruminant Research 73 (2007) 13–26

marily of greater differences among times for I-F versus I-T animals. 4. Discussion 4.1. Experiment 1: carcass and non-carcass pool mass The decrease in mass of many non-carcass tissues of I-F animals as a % of empty BW as the experiment advanced is in accordance with the high maintenance energy cost of these tissues and appreciable energy saved by minimizing their mass. And obviously for the gastrointestinal tract and some other tissues/organs, there is less need for high mass, such as in absorptive surface area, with severely restricted DMI (Johnson et al., 1990). That mass of non-carcass tissues for I-T also decreased as a % of empty BW as the experiment progressed may reflect carcass protein mobilization during the pre-trial period in addition to fat. That is, had initial BCS of I-T animals been slightly greater with higher carcass protein mass, with only or primarily carcass accretion of fat during realimentation, non-carcass tissues as a % of empty BW probably would not have changed during the experiment or could have increased. 4.2. Experiment 1: non-carcass components The majority of change in mass of many internal organs/tissues, such as the reticulo-rumen, in the first 12 weeks of the experiment agrees with other reports of fairly rapid responses to shifts in nutrient intake (Ferrell, 1988; Drouillard et al., 1991; Burrin et al., 1992; Kouakou et al., 1997). As opposed to change with advancing time in mass of many non-carcass organs/tissues of I-F animals, observations of relatively little change or decreases for I-T were not expected. For example, the decrease in reticulo-rumen mass occurred despite substantially greater DMI during the experiment than before. This finding could in part relate to use of a pelletized diet during the experiment. Efficiency of energy metabolism is greater for pelletized versus loose diets (AFRC, 1998). Physical characteristics of pelletized diets perhaps have less stimulatory effects on mass and energy use of the gut (Goetsch et al., 1997), and the relatively short time for ingestion of pelletized diets could have minimized energy use by gastrointestinal tract tissues as well (Osuji, 1974). As noted earlier, during the pre-trial period animals had free-choice access to grass hay and different amounts of a pelletized supplement. Consumption of the largely forage diet by I-T animals may explain greater mass of some tissues

23

like the reticulo-rumen at the beginning of the experiment and digesta fill relative to empty BW compared with I-F animals after consuming the all-pellet diet for 24 weeks. The increase in liver mass for I-T with advancing time was not marked relative to change in DMI. This could have been a consequence of counteracting effects of decreasing mass of other metabolically active non-carcass tissues that impact liver metabolism (e.g., reticulo-rumen and small intestine) (Goetsch, 1998) and need to support energy accretion in other tissues. That liver mass for I-F did not differ between weeks 12 and 24 reflects the importance of hepatic metabolism regardless of the source of nutrients being used for maintenance (i.e., primarily exogenous versus a mixture of endogenous and exogenous). The decrease in internal fat mass for I-F as the experiment progressed, with the value at 24 week much greater than for I-T at 0 week, along with the large magnitude of increase incurred by I-T animals imply relatively high priorities for developing and maintaining this energy depot and a relatively low maintenance cost. The difference in internal fat mass for I-T at week 0 versus I-F at week 24 indicates that a longer or more severe period of nutrient restriction of I-F animals during the experiment would have been required to achieve similar values. Though lengths of the pre-trial period and experiment were not greatly different, before the experiment animals were in pastures with ad libitum access to grass hay during the winter; therefore, I-T animals could have mobilized more energy from internal fat because of greater energy use for activity and thermoregulation and less efficient energy use with a diet based on grass hay versus one pelletized with ingredients of relatively high nutritive value. 4.3. Experiment 1: chemical composition 4.3.1. Carcass The chemical composition of the carcass of I-F animals did not greatly vary among harvest times, with small decreases in concentrations of protein and water and an increased level of fat with advancing time because of protein but not appreciable fat mobilization. It is somewhat surprising that carcass fat concentration for I-F animals, particularly at week 24, was so much greater than for I-T at week 0. However, a factor possibly responsible again is the nature of diets fed in the pre-trial period and during the experiment as impacting the array of absorbed nutrients. The forage-based diet consumed by I-T animals before the experiment presumably would have resulted in absorption of considerably less glucogenic substrates

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(e.g., propionate) than the experimental diet, which could have influenced the propensity to mobilize carcass fat in a manner similar to accretion (Tatum et al., 1988; Murphy et al., 1994; Borton et al., 2005). Hence, future research should consider potential for such effects, which might lead to dietary means of maintaining a relatively high carcass energy concentration despite a limited nutritional plane and BW loss. As a result of appreciable fat accretion by I-T animals, greater in the second versus first half of the experiment (approximately 31.8 versus 21.4 g/day), as well as of protein, the increase in carcass energy concentration from week 0 to 24 was substantial (6 MJ/kg or 85%). However, as noted before, the size of such change depends on initial fat and energy concentrations, which may be influenced by how the nutritional plane is limited. That is, to have extended the experiment and increased nutrient intake by I-F animals would likely have facilitated smaller change in carcass fat and energy concentrations than observed with I-T.

(i.e., 13.6 to 39.6 g/day). In fact, non-carcass fat accretion in weeks 13–24 was greater than in the carcass (i.e., 31.8 g/day).

4.3.2. Non-carcass The increase in non-carcass protein concentration from weeks 0 to 12 for I-F resulted from protein accretion during that time as well as mobilization of fat and water. Based on changes in mass of organs/tissues of the non-carcass pool, it is difficult to ascertain where this protein was accreted. But, it is possible that the concentration of protein in some of the individual non-carcass organs/tissues increased even if mass declined. Also, with such serial harvest experiments a consideration is that different animals give rise to values at each measurement time. The magnitude of this limitation can be minimized, however, through large differences in variables of greatest interest. Despite some non-carcass tissue protein accretion by I-F in weeks 1–12, in weeks 1–24 daily change in protein mass was 0, indicating mobilization of 6.1 g/day in weeks 13–24. This shift was opposite that in non-carcass fat mass, with mobilization in weeks 1–12 decreasing to approximately 4.5 g/day in weeks 13–24. As was true for the carcass, the chemical composition of the non-carcass pool varied with time to a much greater extent for I-T versus I-F animals. There was substantial protein accretion in non-carcass tissues of I-T in weeks 1–12 and a marked increase in the protein concentration from weeks 0 to 12. This accretion may have been slightly greater than necessary since there was a small quantity of protein mobilized from non-carcass tissues in weeks 13–24 (i.e., 1.9 g/day). Corresponding to sizeable differences between 12-week periods in water and protein accretion, there was a dramatic rise from weeks 1–12 to 13–24 in fat accretion by non-carcass tissues

4.3.4. Empty body mobilization/accretion energy concentration A common assumption of many nutrient requirement recommendation systems (e.g., CSIRO, 1990; AFRC, 1998; NRC, 2000, 2001) is that the concentration of energy in tissue accreted is the same as in tissue mobilized when considering similar ranges in body condition or fatness. However, results of this experiment do not support this approach. Because primarily of no or low carcass fat mobilization by I-F, energy concentration in tissue lost was 14.8 and 9.4 MJ/kg (empty BW basis) in weeks 1–12 and 13–24, respectively. These values are considerably less than ones frequently assumed, such as 23.9 MJ/kg of unshrunk BW for goats by AFRC (1998). But, as noted earlier, the nature and severity of the feed restriction and initial body condition in the present experiment may have had impact. For example, a moderate pre-trial nutrient restriction should have minimized need to mobilize carcass protein to support oxidation of fatty acids derived from non-carcass tissues. Also, perhaps a more acetogenic diet than that used during this experiment would have lessened the ability to retain carcass fat, although this would be affected by the available store of internal fat that for I-F animals was not depleted even after 24 week of feed restriction. Nonetheless, concentrations of energy in tissues accreted by I-T, 19.9 and 32.9 MJ/kg in weeks 1–12 and 13–24, respectively, were remarkably greater than in tissue lost by I-F. Thus, to predict the energy concentration in tissue accreted, the severity of the restriction as it affects the depletion of empty body protein and potential

4.3.3. Carcass and non-carcass contributions Overall, non-carcass tissues provided most energy mobilized by I-F animals (70 and 97% in weeks 1–12 and 13–24, respectively). Conversely, non-carcass tissues accounted for 46 and 53% of energy accreted by I-T animals in weeks 1–12 and 13–24, respectively. There appears a much greater propensity for or willingness to mobilize non-carcass than carcass fat to support vital functions. It has been suggested that the water to protein ratio in animals is relatively constant (Murray, 1919; Moulton, 1923). However, similar to as recently shown for beef cattle (Williams, 2005), results of the present experiment indicate that this is not the case for goats. This variability was attributable to non-carcass tissues rather than to the carcass.

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degree of subsequent replenishment should be considered. Interrelated with this is possible impact of animal genotype and production state. For example, Dunshea et al. (1990) estimated an energy concentration in unshrunk BW being lost by lactating Saanen goats between day 38 and 76 of lactation of 23.0 MJ/kg; fat mobilization and a small amount of protein accretion were measured. Dairy goats presumably have less muscle protein available for mobilization compared with meat goats of the present experiment and would in most cases not be subjected to severe feed restrictions while lactating, which suggest a higher energy concentration in mobilized tissue than noted for I-F. Although, Nsahlai et al. (2003) with a database of treatment mean observations from the literature for lactating dairy goats, via a multiple regression approach, predicted an energy concentration in unshrunk BW change (i.e., 11.3 MJ/kg) not greatly different from values for I-F. Concentrations of water and fat in the empty body are in most cases inversely correlated. This was observed for concentrations in carcass tissues lost or gained in this experiment (r = −0.96; P < 0.01). Conversely, concentrations of water and fat in non-carcass tissues accreted or mobilized were not related (r = −0.09; P < 0.66). 4.4. Experiment 1: BCS Ngwa et al. (2007) addressed use of BCS to predict body composition in a companion paper. One interesting finding of the present experiment in relation to equations presented by Ngwa et al. (2007) and the description of how BCS was determined is the lack of appreciable carcass fat mobilization by I-F animals, yet an initially high BCS that decreased during the experiment. These results suggest that with such animals muscle or total peripheral tissue mass might be the primary determinant of BCS rather than fatness per se’ that can be assessed by touching animals with fingers. 4.5. Experiment 1: efficiency of energy use The calculated k for I-F animals reflects highly efficient use of dietary ME for maintenance as a result of the appreciable feed restriction. The value for weeks 13–24, slightly above 100%, suggests that the assumption of a constant efficiency of use of mobilized tissue energy for maintenance was not most appropriate, with perhaps a value higher than 84% in weeks 13–24 needed. The lack of a difference in k of I-T between weeks 1–12 and 13–24 might not be anticipated considering greater empty body fat accretion in weeks 13–24. However, for I-T k represents a combined efficiency of ME use for maintenance

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and energy accretion. In this regard, it is likely that MEm was less in weeks 1–12 than 13–24 because of previously limited MEI, which would have negated or lessened the effect of differences in efficiency of energy use for accretion of fat versus protein (CSIRO, 1990; NRC, 2000). Slightly more efficient use of dietary ME for maintenance by I-T in weeks 1–12 versus 13–24 is supported by k estimated in Experiment 2. 4.6. Experiment 2 Fasting EE for I-F animals reflect the marked effect of level of intake on basal metabolic rate. Fed EE also substantially decreased as the experiment progressed and DMI was reduced. The decline in k for I-F as the experiment advanced may have been due to increasing protein and decreasing fat mobilization, as suggested by results of Experiment 1, because of less efficient use of mobilized energy from protein than fat (Cannas et al., 2004). Converse to change with time in fasting EE in MJ/day by I-F animals, values were similar for I-T. But because of increasing empty BW, values in kJ/kg BW0.75 decreased. This could relate to the small energetic cost of maintaining adipose compared with proteinaceous tissues (Webster, 1980; Emmans, 1994). As noted before, the positive effect on k of increasing fat and decreasing protein accretion by I-T animals as the experiment progressed may have been countered by decreasing MEm . Overall, findings of this experiment, in particular fasting EE, depict need to develop means of predicting MEm that encompass not only current body condition, such as that of NRC (2000), but also either past and target future body condition or the prevailing feeding conditions and specific tissues being mobilized or accreted. 5. Summary and conclusions The energy concentration in empty body tissue mobilized by yearling meat goats with initially high BW and BCS was relatively low, 14.8 and 9.4 MJ/kg in the first and second 12-week periods of feed restriction, respectively. The energy concentration in tissue being gained by meat goats that previously had low BW and BCS was relatively high and differed markedly between periods (19.9 and 32.9 MJ/kg in weeks 1–12 and 13–24, respectively). There appears a high metabolic priority to both retain internal or non-carcass fat by animals previously in high body condition and to develop this energy depot when initially low in body condition. In conclusion, the energy concentration in tissue being mobilized or accreted by yearling meat goats within certain body condition ranges may not necessarily be the same, rather

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impacted by initial animal characteristics and subsequent feeding conditions. Acknowledgment This project was supported by USDA Project Number 03-38814-13923. References AFRC, 1993. Energy and protein requirements of ruminants. In: An Advisory Manual Prepared by the AFRC Technical Committee on Responses to Nutrients. CAB International, Wallingford, UK, pp. 5–55. AFRC, 1998. The Nutrition of Goats. CAB International, Oxon, UK, pp. 41–51. AOAC, 1990. Official Methods of Analysis, 14th ed. Association of Official Analytical Chemists, Washington, DC, pp. 129– 130. ARC, 1980. The Nutrient Requirements of Ruminant Livestock. Commonwealth Agricultural Bureaux, Slough, UK, pp. 2–58. Borton, R.J., Loerch, S.C., McClure, K.E., Wulf, D.M., 2005. Characteristics of lambs fed concentrates or grazed on ryegrass to traditional or heavy slaughter weights. II. Wholesale cuts and tissue accretion. J. Anim. Sci. 83, 1345–1352. Brouwer, E., 1965. Report of sub-committee on constants and factors. In: Blaxter, K.L. (Ed.), Energy Metabolism. Proceedings of the 3rd Symposium. EAAP Publ. No. 11. Academic Press, London, UK, pp. 441–443. Burrin, D.G., Britton, R.A., Ferrell, C.L., Bauer, M.L., 1992. Level of nutrition and visceral organ protein synthetic capacity and nucleic acid content in sheep. J. Anim. Sci. 70, 1137–1145. Cannas, A., Tedeschi, L.O., Fox, D.G., Pell, A.N., Van Soest, P.J., 2004. A mechanistic model for predicting the nutrient requirements and feed biological values for sheep. J. Anim. Sci. 82, 149– 169. CSIRO. Standing Committee on Agriculture. Ruminants Subcommittee, 1990. Feeding standards for Australian Livestock. In: Ruminants. CSIRO Publications, East Melbourne, Australia. Dawson, L.E.R., Steen, R.W.J., 1998. Estimation of maintenance energy requirements of beef cattle and sheep. J. Agric. Sci. 131, 477–485. Drouillard, J.S., Klopfenstein, T.J., Britton, R.A., Bauer, M.L., Gramlich, S.M., Wester, T.J., Ferrell, C.L., 1991. Growth, body composition, and visceral organ mass and metabolism in lambs during and after metabolizable protein or net energy restrictions. J. Anim. Sci. 69, 3357–3375. Dunshea, F.R., Bell, A.W., Trigg, T.E., 1990. Body composition changes in goats during early lactation estimated using a two-pool model of tritiated water kinetics. Br. J. Nutr. 64, 121–131. Emmans, G.C., 1994. Effective energy: a concept of energy utilisation applied across species. Br. J. Nutr. 71, 801–821. Ferrell, C.L., 1988. Contributions of visceral organs to animal energy expenditures. J. Anim. Sci. 66 (Suppl. 3), 23–34.

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