Subcutaneous fat and marbling both increase in beef cattle during the feeding phase but are antagonistic in regard to their contribution to beef carcass value. The objective of this study was to determine whether cellular factors associated with marbling development change with growth stage throughout the feeding period and whether they are correlated to marbling relative to carcass composition. Twenty-four steers of known origin with the cytosine and thymine (CT) leptin genotype were allotted to 3 harvest groups. Six steers per harvest group were harvested at the following predetermined points: 35 d on feed (early feeding period, EF), average live weight of 464 kg (middle feeding period, MF), and 1.17-cm 12th-rib subcutaneous fat thickness (late feeding period, LF). Longissmus muscle samples were collected within 30 min postmortem and snap frozen for real-time PCR and Western blot analysis of lipoprotein lipase, adenosine monophosphate-activated protein kinase α (AMPKα), stearoyl-coenzyme A desaturase (SCD), PPARγ, C/EBP-β, and myostatin. Carcass data were recorded, and LM samples were collected and aged 2, 7, 14, and 21 d postmortem for Warner-Bratzler shear force determination. Carcass composition was estimated by dissection of the 9-10-11 rib section and subsequent proximate analysis of the soft tissue. Intramuscular fat content of the LM increased linearly throughout the feeding period, giving additional support to marbling as an early developing tissue. Expression of AMPKα was found to be downregulated, whereas SCD expression was upregulated in the LF group relative to the first 2 harvest groups. Additionally, SCD and PPARγ were downregulated in the EF group relative to the latter 2 harvest groups. These changes in gene expression resulted in a linear increase in only PPARγ protein abundance, whereas myostatin tended to increase quadratically. A correlation was found between intramuscular fat and PPARγ abundance. This gives further evidence of the importance of adipocyte hyperplasia in increasing marbling. Targeting and increasing PPARγ expression may serve as a mechanism to increase marbling deposition. Last, LF steaks were more tender than MF or EF steaks, indicating improved tenderness with increased days on feed.
There are many cellular regulatory factors that ultimately determine the intramuscular fat, or marbling content and quality of beef carcasses. Identifying factors which play a critical role in the development of intramuscular fat throughout the feeding period and determining how cattle feeders can manipulate these factors will be crucial to continue improving beef quality. Ideally, marbling must increase without excess accumulation of adipose in depots that are undesirable and economically detrimental (subcutaneous and visceral). The results of this study are novel as they show not only what cellular factors play a role in marbling development, but also how their expression and presence change as an animal grows in an American-style production system. The increase in both expression and presence of peroxisome proliferator-activated receptor γ (PPARγ) at the end of the feeding phase suggest the proliferation and differentiation of additional cells to adipocytes is required in order to increase intramuscular fat content. This does not mean that adipocyte filling (lipogenesis) does not play a key role as well. However marbling content will reach a plateau without the recruitment of additional adipocytes. While it has been previously established that intramuscular adipocytes have a pattern of metabolism unique to other adipocytes, further research into how the metabolism of intramuscular fat differs from other fat depots and how this metabolism changes throughout the feeding phase will enhance the ability to produce high quality carcasses while limiting undesirable carcass fat.
Crossbred pigs (Fast Genetics 276 × PIC 800; n = 2,332; initial BW = 24.5 ± 1.6 kg) were used in two, 84-d growth trials to evaluate effects of an additional water source (fixed double nipple waterer) to a wet/dry feeder on growing-finishing pig performance. Pigs were assigned randomly to 1 of 2 treatments with 27 to 30 pigs per pen and 40 pens per treatment. Pens were equipped with a wet/dry feeder (SDI, drop shelf wet/dry feeder) or with a wet/dry feeder in combination with the additional water source. Marketing began on d 84 of each trial so the highest pig demands on feeders and waterers were assumed to occur from d 0 to 84 when all pigs were present in each pen. Growth data were analyzed using the GLIMMIX procedure of SAS and removals, mortalities, and total removals were analyzed using a Chi-square test in SAS version 9.4 (SAS Institute Inc., Cary, NC). No significant interactions between trial and water treatment were observed, thus data were combined using water treatment as a fixed effect and trial as a random effect. No differences were observed for body weight on d 84, average market weight, or number of removals, mortalities, or total pigs removed (Table). Similarly, no evidence for differences in overall average daily gain, average daily feed intake, or gain efficiency were observed regardless of an additional water source. However, pigs given access to a supplemental water source displayed a numeric increase in water disappearance per pig compared to pigs in pens with only wet/dry feeders. In conclusion, addition of a fixed double nipple waterer to wet/dry feeders did not influence growth performance of growing-finishing pigs.
Crossbred pigs (Fast Genetics 276 × PIC 800; n = 2,388; initial BW = 74.1 ± 2.0 kg) were used in two, 63-d growth trials to evaluate the addition of a water source (fixed double nipple waterer) to wet/dry feeders on finishing pig performance. Pigs were assigned randomly to 1 of 2 treatments with 27 to 30 pigs per pen and 40 pens per treatment. Pens were equipped with a wet/dry feeder (SDI, drop shelf wet/dry feeder) with no supplemental water or a wet/dry feeder with a supplemental water source available from 74 kg BW until marketing. Growth data were analyzed using the GLIMMIX procedure with repeated measures over time. The model included fixed effects of water treatment, trial, and time with all possible two-way interactions. Removals, mortalities, and total removals were analyzed using a binomial distribution. No differences (P > 0.05) in body weight were observed initially or at the last marketing event between water source treatments; however, a supplemental water source tended (P = 0.061) to decrease average market weight compared to pigs not given a supplemental waterer (Table). Overall average daily gain (ADG) was lower (P = 0.011) and average daily feed intake (ADFI) was decreased (P = 0.002) for pigs given a supplemental waterer compared to pigs only drinking from a wet/dry feeder. No differences were observed for the percentage of mortalities, pigs removed, or total removals (P > 0.05) regardless of treatment. Finally, daily water disappearance was 2.5 liters greater for pigs with a supplemental waterer compared to pigs with no supplemental waterer. In conclusion, the addition of a supplemental water source to wet/dry feeders decreased growth performance.
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