Limit Feeding: Small Change With Sizable Impacts

By Jane Fyksen, Crops Editor
Wednesday, June 18, 2008 10:42 AM CDT

Dairy producers typically have generous inventories of corn silage n whether they want to or not. The tendency is to feed over the energy requirements of their heifers, predisposing them to over-conditioning and jeopardizing future lactation performance.

Many have cut the energy density of the diet with low-energy forage, notably ground straw, which, of course, has gotten pretty expensive. Limiting dry matter and control caloric intake is a viable alternative, according to UW dairy scientist Pat Hoffman, who’s been studying limit feeding from a slightly different angle than Penn State University’s Judd Heinrichs, whose work was featured last week in this series.

Hoffman tells Agri-View that besides extending the feed inventory and saving on the feed bill, limit feeding heifers is a way to reduce a dairy’s volume of manure and its “environmental footprint.” Trimming a couple pounds of dry matter per day from what each heifer on your farm is consuming can roughly translate into 10 pounds less manure from every heifer daily. “That’s a lot of manure. It really is,” says Hoffman, referring especially to the cumulative impact on bigger dairies. “It gets into tanker loads of manure real quick.”

Briefly describing the results of limit feeding studies at the UW thus far, Hoffman says the practice didn’t impact future milk production of those heifers. They saw increased feed efficiency and metabolic efficiency and less manure. Hoffman also observed some behavior changes in limit fed heifers, which, he notes, are very manageable.

“Historically, research has been focused on feeding heifers higher energy diets to reduce calving age” to shorten the rearing period and reduce feed costs. “although this strategy has the potential to lead to an earlier return on feed investment, decreasing the calving age frequently results in a decrease in lactation performance,” Hoffman discusses, noting that the alternative strategy to cut feed costs is to feed higher energy diets and limit the amount fed, controlling average daily gain (ADG), which could effectually yield a calving age and body condition score similar to feeding high forage diets. Limit feeding, he notes, saves on the feed bill and trims manure-handling costs while preserving “the rearing period time course, which, to date, has been difficult to alter without negative health and production effects.”

At the UW, Hoffman and colleagues explored a simple limit feeding system for bred replacement heifers. Bred Holstein heifers were fed three diets. Diet “C-100” was the control; heifers were fed “ad lib.” Diet “L-90” was limited to 90 percent of intake, while “L-80” was limited to 80 percent. The three diets contained 67.5 percent, 70 percent and 73.9 percent total digestible nutrients (TDN), respectively. But heifers fed the 70 and 73.9 percent TDN diets were limit fed at 90 and 80 percent of their intake potential. Limit feeding resulted in heifers being fed less DM per day, but total calories consumed per day were equal.

“We did not observe any differences in the size or body condition scores of the heifers after a 111-day feeding period,” he reports. “The limit feeding regimen, however, resulted in a 25 percent improvement in feed efficiency n and heifers excreted significantly less manure.”

“We observed no effects of limit feeding heifers on calf BW (bodyweight) or dystocia index,” he continues. The dystocia index was: 1, no problem; 2, slightly problem; 3, needed assistance; 4, considerable force; 5, extremely difficult.

They did observe “a numerical trend in improved milk yield,” but “true lactation performance was similar between control and limit fed heifers.”

Here’s a more detailed comparison of the three diets on a DM basis:

- C-100 (control) n 94.3 percent forage, 5.7 percent concentrate, 47.3 percent NDF; 21.3 pounds of DM intake per day (2.42 pounds crude protein, 10.06 pounds NDF and 9.4 pounds NE or Mcals)

- L-90 n 80.3 percent forage, 19.7 percent concentrate; 41.8 percent NDF; 19.9 pounds of DM intake per day (2.54 pounds CP, 8.29 pounds NDF, 9.4 pounds NE or Mcals)

- L-80 n 62.7 percent forage, 37.3 percent concentrate, 35.6 percent NDF; 18.3 pounds of DM intake per day (2.57 pounds CP, 6.5 pounds NDF, 9.5 pounds NE or Mcals).

Here’s how the heifers did:

- C-100 n Initial body weight, 1,036 pounds, and final BW, 1,220; 13.2 pounds of DM per pound of gain (feed efficiency); 7.7 pounds DM excretion (manure) per day; dystocia index 2.2; calf BW, 91.4 pounds; postpartum BW, 1,238 pounds

- L-90 n Initial body weight, 1,021 pounds, and final BW, 1,234; 10.7 pounds of DM per pound of gain (feed efficiency); 6.9 pounds DM excretion (manure) per day; dystocia index, 2.1; calf BW, 93.3 pounds; postpartum BW, 1,245 pounds

- L-80 n Initial body weight, 1,011 pounds, and final BW, 1,217 pounds; 11.1 pounds of DM per pound of gain (feed efficiency); 5.8 pounds DM excretion (manure) per day; dystocia index, 1.9; calf BW, 95.1 pounds; postpartum BW, 1,275 pounds.

As for lactation performance (up to 150 days in milk), the diets shook out like this:

- C-100 n 68.8 pounds of milk per day; 3.89 percent fat; 2.87 percent protein

- L-90 n 68.9 pounds of milk per day; 2.74 percent fat; 2.85 percent protein

- L-80 n 72.4 pounds of milk per day; 3.68 percent fat; 2.89 percent protein.

Hoffman highlights differences between UW and Penn State work in limit feeding. The UW focused on 1,000-pound bred heifers with a short experimental period (111 day). Penn State looked at heifers weighing 275 pounds; they were limit fed 254 days and then fed a common diet post-puberty. The level of concentrate in the limit fed diet (75 percent) was higher than the level of concentrate Hoffman fed to bred heifers (37 percent).

At Penn State, limit feeding 300-pound Holstein heifers the diet containing 25 percent forage as compared to feeding the diet containing 75 percent forage ad lib resulted in no differences in ADG or skeletal growth of heifers. Heifers reached puberty at the same age and had similar reproductive performance. Heifers calved at the same age. But the limit fed heifers had numerically higher BW at calving and lost more BW after calving. As with other studies, limit fed heifers produced numerically higher amounts of milk with similar milk composition.

“It is important to recognize the uniqueness of each of these studies,” Hoffman stresses. “In the Wisconsin study, heifers were limit fed post puberty, while the heifers in the Penn State study were limit fed pre-puberty. Both limit feeding strategies resulted in similar animal performance,” he says, adding that “to date, there are no data for limit feeding heifers throughout the majority of the rearing period.”

Hoffman noted some changing in the behavior of limit fed heifers. Heifers vocalized “to a minor extent” for about a week at the start, with vocalization diminishing thereafter. The heifers primarily bellowed immediately prior to feeding.

“Eating time is logically reduced when heifers are limit fed, but heifers appear to compensate for reduced eating times by standing more, which ultimately reduces lying times,” Hoffman notes, stressing that the behavioral changes he observed were “subtle and manageable.”

Specifically, here’s how the diets compared:

- C-100 n Eating (percent of time), 19.3; standing (percent of time), 19.6; lying (percent of time), 60.9; vocalization (percent of time), 0.02; eating (hours per day), 2.3; standing, 4.7 hours, lying, 14.6 hours. Note that time associated with involuntary behavior, like during barn cleaning or blood sampling, wasn’t recorded, so the percent of time and hours of time don’t equal 100 and 24, respectively.

- L-90 n Eating, 15.7 percent of time; standing, 24.4 percent; lying, 59.8 percent ; vocalization, 0.04 percent; eating, 1.9 hours; standing, 5.8 hours; lying, 14.4 hours

- L-80 n Eating, 10.3 percent of time; standing, 32.9 percent; lying, 56.7 percent; vocalization, 1.1 percent; eating, 1.2 hours; standing, 7.9 hours; lying, 13.6 hours.

He observed some “undocumented quirks” in heifer behavior, too, as a result of limit feeding. Heifers were fed in pens of six heifers. “At the time of the experiment, we failed to anticipate changes in bunk (i.e. eating) behavior and did not quantify these issues,” he admits, noting that they did observe subtle eating behavior changes in heifers limited to 80 to 90 percent of maximum intake. Hoffman stresses that he didn’t see “overly aggressive” eating behavior.

However, what he did see was that heifers n even when limit fed n always sort feed, like all dairy cattle do. Fed on a flat feeding surface, a large portion of the diet is pushed out of reach by the heifers. If they haven’t reached “fill” (i.e. satiety), they’ll aggressively reach for the feed they’d pushed too far forward. “The long term effect of this behavior on foot and leg health is not known,” he notes.

Hoffman says they simply pushed remaining feed up more frequently n an hour after the heifers were fed.

“We would caution that increased feed push ups may be required when limit feeding heifers in a flat manger,” this UW dairy scientist states.

Another undocumented behavior change Hoffman saw is that heifers appear to become acclimated to limit feeding and their eating behaviors carry over for a short time after limit feeding is discontinued. Afterwards, UW researchers transitioned the heifers to a common high bulk, high NDF diet. For five to seven days, they ate as if they were still being limit fed. Additional ruminal distention was obvious, says Hoffman, suggesting that heifers have the ability to rapidly increase rumen volume, just as quick and rapid extension of rumen volume has been well documented in lactating dairy cows.

Hoffman says producers need adequate bunk space to limit feed. All heifers need full access to feed, because heifers fed to 80 percent of intake potential will consume all feed available within two to three hours.

“Lack of adequate bunk space could result in displacements at the bunk and ultimately result in uneven ADG,” he notes, adding that he saw small numerical increases in ADG variance when heifers were limit fed, but that variance wasn’t significant when 1,000-pound heifers were allowed 24 inches of bunk space per heifer.

Hoffman says the critical lower limit of bunk space per heifer for limit feeding isn’t known.

Finally, he notes that limit feeding can’t be implemented where “edible bedding” such as straw or corn stalks, or grass, is used, as heifers will eat bedding to reach satiety.

Hoffman tells Agri-View he thinks limit feeding is “best suited” for heifers over a year of age, because of their “notoriously poor feed efficiency” and “because of their size,” they eat quite a bit. He thinks limit feeding those older heifers 80 percent of maximum intake potential is “about as low as you want to go.” Doing 90 percent will save feed and “you’ll barely notice it” in terms of the difference it takes in your heifer rearing system. However, a couple pounds of feed will be saved per heifer per day.

“It’s a small management change n not anything real dramatic, but in the course of many days over many animals,” it’ll improve your heifer rearing bottom line, says Hoffman. As important these days, it’ll also mean less manure to handle.

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