Figure 2. Expression of mRNA (relative fold change) in genes associated with pregnancy establishment in conceptus and endometrial samples collected on day 15 of gestation, and whole blood collected on day 20 of gestation from
B. indicus cows receiving or not (CON; n = 10) Ca soaps of soybean oil (CSSO; n = 10) after artificial insemination. PGES =
prostaglandin E synthase;
IFN-τ = interferon-tau; COX-2 = cyclooxygenase-2;
ISG15 = interferon-stimulated gene 15;
MX2 = myxovirus resistance 2;
OAS =
20,
50-
oligoadenylate synthetase. All values reported are least square means ± standard error (represented as error bars). Within variable, **
p < 0.01 and *
p ≤ 0.05. Adapted from Cipriano et al.
[20].
Our initial efforts in characterizing the benefits of omega-6 FA to cattle reproduction were conducted with
B. indicus cows reared in tropical conditions
[15,16,18,20][15][16][18][20]. Pregnancy establishment and overall reproductive physiology differ between
B. indicus and
B. taurus females
[25], and FA composition differs between tropical and temperate feed ingredients. Hence, Brandão et al.
[26] conducted two trials evaluating omega-6 FA supplementation via CSSO to
B. taurus cows in temperate conditions. In the first trial, grazing Angus cows were supplemented with 100 g/day of CSSO or prilled saturated fat (iso-caloric and iso-lipidic control; CON+) for 21 days after AI. Similar to the findings from Lopes et al.
[15[15][16],
16], pregnancy rates following AI were increased by 17% in cows supplemented with omega-6 FA (). The companion trial focused on conceptus- and endometrial-derived responses that mediate pregnancy signaling to maternal tissues with a design similar to Cipriano et al.
[20], using Angus × Hereford cows that received 100 g/day of CSSO or CON+ beginning after AI. Supplementing omega-6 FA upregulated mRNA expression of IFN-τ by the conceptus and ISG in the whole blood, but did not increase conceptus length (11.3 vs. 11.4 cm for CSSO and CON, respectively) and mRNA expression of
prostaglandin E synthase. Conceptus length across treatments was 11.4 ± 1.9 cm in Brandão et al.
[26] and 2.4 ± 0.5 cm in Cipriano et al.
[20], suggesting that
B. taurus conceptus may be at an advanced stage of elongation on day 15 of gestation compared with
B. indicus conceptus, and past the stage in which omega-6 FA impacts conceptus growth and expression of
prostaglandin E synthase. Nevertheless, results from Brandão et al.
[26] confirmed that omega-6 FA supplementation via CSSO to
B. taurus cows also upregulated IFN-τ synthesis by the conceptus during the pregnancy recognition period, leading to increased pregnancy rates following fixed-time AI.
Table 2.
Pregnancy rates and expression of mRNA (relative fold change) of genes associated with pregnancy establishment in
B. taurus
cows receiving Ca soaps of soybean oil (CSSO) or prilled saturated fat (CON+) after artificial insemination. Values reported are least square means ± standard error. Adapted from Brandão et al. [26] 1
.
Item |
CON+ |
CSSO |
p = |
Pregnancy rates to AI (n = 11/treatment), % |
51.7 ± 4.1 |
60.2 ± 4.2 |
0.01 |
Physiological responses (n = 9/treatment) |
|
|
|
Endometrium, mRNA expression |
|
|
|
Cyclooxygenase-2 |
5.11 ± 1.32 |
4.88 ± 1.33 |
0.89 |
Prostaglandin E synthase |
7.40 ± 1.05 |
5.76 ± 1.15 |
0.30 |
Conceptus, mRNA expression |
|
|
|
Interferon-tau |
12.1 ± 3.6 |
21.3 ± 3.4 |
0.05 |
Prostaglandin E synthase |
2.50 ± 0.49 |
2.22 ± 0.48 |
0.69 |
Whole blood, mRNA expression |
|
|
|
Interferon-stimulated gene 15 |
29.8 ± 4.9 |
43.1 ± 4.3 |
0.04 |
Myxovirus resistance 2 |
20.1 ± 2.8 |
20.2 ± 2.5 |
0.98 |
20,50-oligoadenylate synthetase |
18.3 ± 2.9 |
26.8 ± 2.6 |
0.03 |
Collectively, supplementing omega-6 FA via CSSO increased incorporation of these FA into maternal and embryonic tissues and promoted IFN-τ synthesis by the conceptus during the maternal pregnancy recognition period, leading to increased pregnancy success in beef cows. These outcomes were generated across several research trials using nearly 6000 beef cows from different subspecies and managed in different environments, and were independent of the energy contribution of omega-6 FA given that iso-caloric and iso-lipidic control supplements were included. Hence, omega-6 FA supplementation is a nutritional alternative to enhance the reproductive efficiency of
B. taurus and
B. indicus beef cows reared in temperate and tropical environments.
3. Supplemental Omega-6 FA and Developmental Programming
The embryonic, fetal, and neonatal periods are the stages of life in which most developmental processes occur
[27]. Nutrient supply during these periods exerts long-term consequences on the growth, development, and metabolic functioning of the offspring
[28], leading to the concept of developmental programming
[29]. Fetal developmental is sensitive to maternal nutrient status from oocyte maturation to parturition
[30[30][31],
31], and developmental plasticity remains susceptible to environmental stimuli during early postnatal life
[32]. Dietary FAs provide a specific opportunity to nutritionally modulate developmental programming, as they differentially regulate expression of genes across metabolic tissues. For example, omega-3 FA limits adipose tissue accumulation by suppressing adipocyte differentiation
[33[33][34],
34], whereas omega-6 FA has been described as proadipogenic
[35,36][35][36]. The fetal stage is critical for skeletal muscle and intramuscular adipocyte development
[37,38][37][38]; hence, omega-6 FA supplementation during gestation can potentially enhance adipogenesis and thereby sites for marbling formation later in life
[39].
4. Supplemental Omega-6 FA to Growing and Finishing Cattle
Weaning and feedlot receiving are two of the most stressful events in the beef production cycle, when cattle are exposed to a variety of physiological and physical stressors, including road transport, exposure to novel diets and environments, and comingling with new animals
[63][40]. The combination of all of the stressors stimulates neuroendocrine and inflammatory reactions that directly impair cattle immunocompetence and productivity, leading to BRD incidence and reduced performance upon feedlot arrival
[64][41]. Hence, strategies to increase the immunocompetence of cattle during the initial phases of the feedlot are warranted, including the use of omega-6 FA based on its immunomodulatory properties
[65][42]. Research from our group demonstrated that omega-6 FA supplementation via CSSO to cattle upon feedlot arrival decreased plasma concentrations of inflammatory markers, but reduced feed intake and subsequent cattle ADG
[8]. For this reason, our group evaluated omega-6 FA supplementation prior to feedlot arrival, by supplementing CSSO during a post-weaning preconditioning program
[9]. Steers supplemented with omega-6 FA via CSSO during preconditioning had a greater feedlot-received ADG, which was attributed to reduced plasma concentrations of proinflammatory cytokines (). Moreover, CSSO steers had improved carcass marbling upon slaughter, which was associated with greater ADG upon feedlot arrival and potentially with metabolic imprinting effects, as omega-6 FA was supplemented when steers were 6 months old
[9]. Hence, omega-6 FA supplementation prior to feedlot arrival should also be considered as a nutritional intervention to improve initial health and performance of feedlot cattle.
Table 63.
Performance and health responses from steers supplemented or not (CON; n = 6) with Ca soaps of soybean oil (CSSO; n = 6) for 28 days prior to feedlot arrival (day 0). Values reported are least square means ± standard error. Adapted from Cooke et al. [9].
Item |
CON |
CSSO |
p = |
Plasma tumor necrosis alpha, pg/mL (log) |
|
|
|
Day 0 (arrival) |
1.74 ± 0.21 |
1.91 ± 0.21 |
0.58 |
Day 1 |
1.88 ± 0.23 |
2.00 ± 0.22 |
0.67 |
Day 3 |
2.23 ± 0.20 |
1.55 ± 0.20 |
0.03 |
Feedlot average daily gain, kg/d |
|
|
|
Initial phase (day 1 to 144) |
1.17 ± 0.02 |
1.25 ± 0.02 |
0.02 |
Final phase (day 145 to slaughter) |
2.10 ± 0.05 |
2.09 ± 0.05 |
0.86 |
Carcass traits |
|
|
|
Hot carcass weight, kg |
394 ± 6 |
402 ± 6 |
0.31 |
Longissiumus muscle area, cm2 |
94.7 ± 1.5 |
92.0 ± 1.6 |
0.23 |
Yield grade |
3.16 ± 0.10 |
3.48 ± 0.11 |
0.04 |
Marbling |
444 ± 18 |
515 ± 19 |
0.01 |
Backfat, cm |
1.55 ± 0.06 |
1.63 ± 0.06 |
0.38 |
Beef cattle are typically backgrounded on pasture after weaning in areas where forage is available for grazing
[66][43], although supplemental nutrients are often required in this practice to meet the requirements of growing cattle
[67][44]. Hess et al.
[5] reviewed multiple studies in which omega-6 FA was supplemented to grazing cattle, but using grains and oilseeds highly susceptible to ruminal biohydrogenation
[10]. To fill this gap in knowledge, Cappellozza et al.
[68][45] evaluated performance and nutrient intake of grazing
B. indicus bulls supplemented with omega-6 FA via CSSO. In this study, ADG was increased in bulls offered a grain-based supplement at 0.3% of their body weight fortified with omega-6 FA compared with bulls receiving an iso-caloric and iso-nitrogenous control supplement (0.92 vs. 0.81 kg/day, respectively). These authors also noted that bulls supplemented with omega-6 FA consumed less water (4.11 vs. 4.96% of body weight), and hypothesized that this outcome was due to reduced ruminal caloric increment from inclusion of CSSO into the supplement
[68][45]. More specifically, CSSO partially replaced corn to maintain the supplement’s iso-caloric and iso-nitrogenous status, whereas ruminal fermentation of starch resulted in greater heat production compared with rumen-inert fats
[68,69][45][46].
Another area of limited research is the inclusion of omega-6 FA into feedlot diets, as these FA from natural sources can disrupt ruminal function, feed intake and efficiency, and overall cattle performance
[5]. The use of CSSO may partially alleviate these concerns, as supplementing Ca soaps of cottonseed oil improved feed efficiency of feedlot
B. indicus bulls compared with cohorts receiving isocaloric and isonitrogenous diets
[70][47]. Accordingly, Nascimento et al.
[70][47] investigated the inclusion of omega-6 FA via CSSO, or a mixture of palm, soybean, and cottonseed oils fed as Ca soaps into feedlot diets (CSMIX). Supplemented CSSO or CSMIX increased energy intake, feed efficiency, ADG, and carcass merit of
B. indicus finishing bulls compared with cohorts not receiving supplemental fat (). In turn, cattle performance and carcass traits were not improved by omega-6 FA supplementation via CSSO compared with the saturated + monounsaturated FA provided by the CSMIX (). Therefore, omega-6 FA inclusion via CSSO to feedlot diets improved cattle performance and efficiency by increasing the energy density of the diet, whereas a combination of saturated + monounsaturated FA appears to be more favorable for feedlot productivity and carcass quality
[71,72][48][49].
Table 74. Performance and carcass traits of feedlot bulls supplemented or not (CON; n = 16) with Ca soaps of soybean oil (CSSO; n = 16) or a mixture of palm, soybean, and cottonseed oils (CSMIX; n = 15) until slaughter. Values reported are least square means ± standard error. Adapted from Nascimento et al. [70] Performance and carcass traits of feedlot bulls supplemented or not (CON; n = 16) with Ca soaps of soybean oil (CSSO; n = 16) or a mixture of palm, soybean, and cottonseed oils (CSMIX; n = 15) until slaughter. Values reported are least square means ± standard error. Adapted from Nascimento et al. [47] 1
.
Item |
CON |
CSSO |
CSMIX |
C1 |
C2 |
Performance |
|
|
|
|
|
Average daily gain, kg/d |
1.14 ± 0.04 |
1.37 ± 0.05 |
1.48 ± 0.05 |
<0.01 |
0.11 |
Feed efficiency, g/kg |
156 ± 3 |
168 ± 3 |
183 ± 3 |
<0.01 |
<0.01 |
Final body weight, kg |
476 ± 6 |
508 ± 7 |
524 ± 7 |
<0.01 |
0.13 |
Carcass traits |
|
|
|
|
|
Hot carcass weight, kg |
268 ± 4 |
284 ± 4 |
297 ± 4 |
<0.01 |
0.03 |
Longissiumus muscle area, cm2 |
67.8 ± 1.88 |
70.4 ± 1.94 |
75.4 ± 1.94 |
0.04 |
0.08 |
Backfat, cm |
0.318 ± 0.035 |
0.439 ± 0.039 |
0.448 ± 0.040 |
0.01 |
0.87 |
5. Conclusions
This review compiled recent research on omega-6 FA supplementation via CSSO to beef cattle, and its benefits to production efficiency across different environments and sectors of the beef industry. Supplementing omega-6 FA increased the reproductive efficiency of beef cows by promoting the processes associated with early pregnancy establishment. Omega-6 FA also elicited positive effects during periods of developmental plasticity, such as gestation and early postnatal life. Supplementing omega-6 FA to beef cows during late gestation resulted in alterations in tissue differentiation and improved health and productivity of offspring. Similar effects on developmental programming were noted when omega-6 FA was supplemented to young calves. Lastly, supplementing omega-6 FA to growing cattle receiving forage-based diets resulted in enhanced immunocompetence, growth, and carcass merit, although such benefits were not evident when omega-6 FA was provided to feedlot cattle consuming high-concentrate diets. Collectively, this review provides research-based evidence that omega-6 FA supplementation via CSSO is a sustainable approach to improve beef production efficiency.